www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - Foreach Range Statement

reply Xinok <xnknet gmail.com> writes:
I'd like to suggest my own design for this. I originally posted it to 
the unofficial wish list to see how many votes it would get:
http://all-technology.com/eigenpolls/dwishlist/index.php?it=142

The arguments are basically the same as the range / xrange functions in 
Python.

The only thing my design doesn't provide is foreach_reverse. Python 
automatically reverses provided the values are correct (xrange(10, 0, 
-1)), but this would cause a small overhead in the loop.


for i(100)
foreach(i; 0..100)
for(int i = 0; i < 100; ++i)

for i(100, 200)
foreach(i; 100..200)
for(int i = 100; i < 200; ++i)

for i(200, 400, 2)
-- Not possible using foreach
for(int i = 200; i < 400; i += 2)
Jul 22 2007
parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Xinok" <xnknet gmail.com> wrote in message 
news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.
Jul 22 2007
next sibling parent "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Jarrett Billingsley" <kb3ctd2 yahoo.com> wrote in message 
news:f816re$96v$1 digitalmars.com...

I should really check .announce before posting things here XD 
Jul 22 2007
prev sibling parent reply Bill Baxter <dnewsgroup billbaxter.com> writes:
Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...
 
 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb
Jul 22 2007
parent reply Reiner Pope <some address.com> writes:
Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free. What's wrong with adding that to the language, but templated and with nice syntax? type name literal int..int (range of int) 1..5 int..double (range of int to double) 1..5.0 int..int:int (stepped range) 5..1:-1 (I'm not sure of the use of mixed-type ranges, but this seems the most intuitive syntax. Since most ranges are probably of one type, how about allowing a symbol to denote "same type again". Any of the following could mean int..int: int..#, int.._, int..$) As several people have pointed out, this also fixes mixed indexing/slicing problems for multi-dimensional arrays. Reiner
Jul 23 2007
next sibling parent reply Don Clugston <dac nospam.com.au> writes:
Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free. What's wrong with adding that to the language, but templated and with nice syntax? type name literal int..int (range of int) 1..5 int..double (range of int to double) 1..5.0 int..int:int (stepped range) 5..1:-1 (I'm not sure of the use of mixed-type ranges, but this seems the most intuitive syntax. Since most ranges are probably of one type, how about allowing a symbol to denote "same type again". Any of the following could mean int..int: int..#, int.._, int..$)

I don't think it make sense to have mixed type ranges. The normal promotion rules should apply. However... Floating-point ranges are tricky. Should they be open-ended, or closed-ended? Consider -real.infinity..real.infinity Are the infinities part of the range? If not, how do you specify a range which includes infinity? I think the convention "first_element .. last_element+1" cannot be extended to negative and floating-point numbers without creating an inconsistency. Which is quite unfortunate.
Jul 23 2007
parent reply Bill Baxter <dnewsgroup billbaxter.com> writes:
Don Clugston wrote:
 Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free. What's wrong with adding that to the language, but templated and with nice syntax? type name literal int..int (range of int) 1..5 int..double (range of int to double) 1..5.0 int..int:int (stepped range) 5..1:-1 (I'm not sure of the use of mixed-type ranges, but this seems the most intuitive syntax. Since most ranges are probably of one type, how about allowing a symbol to denote "same type again". Any of the following could mean int..int: int..#, int.._, int..$)

I don't think it make sense to have mixed type ranges. The normal promotion rules should apply. However... Floating-point ranges are tricky. Should they be open-ended, or closed-ended?

Both Matlab and Numpy have floating point ranges. Matlab ranges are always inclusive, so 1:2.1:7.3 gives you 1.0, 3.1, 5.2, 7.3. Python ranges are always non-inclusive, so it gives you 1.0,3.1,5.2.
 Consider
 -real.infinity..real.infinity
 Are the infinities part of the range? If not, how do you specify a range 
 which includes infinity?

Does it matter that much? I suppose it would be cool if it did something really consistent, but Numpy just craps out and gives you an empty list, and Matlab raises an error "Maximum variable size allowed by the program is exceeded".
 I think the convention "first_element .. last_element+1" cannot be 
 extended to negative and floating-point numbers without creating an 
 inconsistency. Which is quite unfortunate.

In Python the last_element..first_element inclusive case is handled by omissions. 10:0:-1 --- 10 downto 1, inclusive -- doesn't include 0 10::-1 --- 10 downto last one - includes 0 For D I guess that might become 10..$:-1 but $ would have to become something context sensitive, rather than just a synonym for .length. Which I guess is the same as saying you'd have to introduce an inconsistency, or at least a less strict form of consistency, to the interpretation of $. --bb
Jul 23 2007
next sibling parent reply Reiner Pope <some address.com> writes:
Bill Baxter wrote:
 Don Clugston wrote:
 I think the convention "first_element .. last_element+1" cannot be 
 extended to negative and floating-point numbers without creating an 
 inconsistency. Which is quite unfortunate.


I'm not sure of the problem with negative integers is. Even for negative integers x, the identity still holds, that the following two expressions are equivalent: a <= x a < x+1 But the floating point issue is a bummer. And it's also a bit silly for chars. To test whether c is a digit, you would have to write: c in ['0'..'9'+1] which looks a little silly.
 
 In Python the last_element..first_element inclusive case is handled by 
 omissions.
   10:0:-1  --- 10 downto 1, inclusive -- doesn't include 0
   10::-1 --- 10 downto last one - includes 0
 
 For D I guess that might become
    10..$:-1
 but $ would have to become something context sensitive, rather than just 
 a synonym for .length.  Which I guess is the same as saying you'd have 
 to introduce an inconsistency, or at least a less strict form of 
 consistency, to the interpretation of $.
 

To me, it isn't obvious that $==0 in your example. But I think the real value of $ is in multi-dimensional arrays, because without it you would get something like: int[,,] a = ...; int[,,] my_slice = a[1..$, 1..$, 1..$]; int[,,] my_slice_ugly = a[1..a.length[0], 1..a.length[1], 1..a.length[2]]; To support that, I would use Andrei's suggested grammar, but instead of $ translating into a.length, the compiler should first try a.length(0) or a.length(1), etc, where the parameter is the parameter number where the $ occurs. (It's a hack, I know, but I think it's better than $ generating a delegate...) -- Reiner
Jul 23 2007
next sibling parent Oskar Linde <oskar.lindeREM OVEgmail.com> writes:
Reiner Pope skrev:

 To me, it isn't obvious that $==0 in your example. But I think the real 
 value of $ is in multi-dimensional arrays, because without it you would 
 get something like:
 
   int[,,] a = ...;
   int[,,] my_slice = a[1..$, 1..$, 1..$];
   int[,,] my_slice_ugly = a[1..a.length[0], 1..a.length[1], 
 1..a.length[2]];
 
 To support that, I would use Andrei's suggested grammar, but instead of 
 $ translating into a.length, the compiler should first try a.length(0) 
 or a.length(1), etc, where the parameter is the parameter number where 
 the $ occurs. (It's a hack, I know, but I think it's better than $ 
 generating a delegate...)

The way I have handled multidimensional slices is to make ranges including $ distinct types, like: http://www.csc.kth.se/~ol/indextypes.d All those distinct types might be overkill, but saves some unnecessary parameter passing and calls to .length(x). If $ in index expressions could behave equivalent to "end" does in that sample, it would be great. Having $ translate into a.length would mean range expressions containing $ could never become first class citizens. With the types in indextypes.d one can write: auto a = range(0, end-1); auto b = range(end-10, end); auto c = 7; auto B = A[a,b,c]; It would be neat to have something at least close to this with built in ranges. -- Oskar
Jul 23 2007
prev sibling parent reply Sean Kelly <sean f4.ca> writes:
Reiner Pope wrote:
 Bill Baxter wrote:
 Don Clugston wrote:
 I think the convention "first_element .. last_element+1" cannot be 
 extended to negative and floating-point numbers without creating an 
 inconsistency. Which is quite unfortunate.


I'm not sure of the problem with negative integers is. Even for negative integers x, the identity still holds, that the following two expressions are equivalent: a <= x a < x+1 But the floating point issue is a bummer. And it's also a bit silly for chars. To test whether c is a digit, you would have to write: c in ['0'..'9'+1] which looks a little silly.

Perhaps there should be an operator for inclusive vs. exclusive ranges. Something like: c in ['0' -> '9'] Not ideal, I know. Sean
Jul 23 2007
parent Bill Baxter <dnewsgroup billbaxter.com> writes:
Sean Kelly wrote:
 Reiner Pope wrote:
 Bill Baxter wrote:
 Don Clugston wrote:
 I think the convention "first_element .. last_element+1" cannot be 
 extended to negative and floating-point numbers without creating an 
 inconsistency. Which is quite unfortunate.


I'm not sure of the problem with negative integers is. Even for negative integers x, the identity still holds, that the following two expressions are equivalent: a <= x a < x+1 But the floating point issue is a bummer. And it's also a bit silly for chars. To test whether c is a digit, you would have to write: c in ['0'..'9'+1] which looks a little silly.

Perhaps there should be an operator for inclusive vs. exclusive ranges. Something like: c in ['0' -> '9'] Not ideal, I know. Sean

In previous discussion it was mentioned that Ruby has a..b and a...b as inclusive and exclusive ranges, respectively. The previous thread also threw around a lot of possible alternative syntaxes. --bb
Jul 23 2007
prev sibling parent reply Don Clugston <dac nospam.com.au> writes:
Bill Baxter wrote:
 Don Clugston wrote:
 Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free. What's wrong with adding that to the language, but templated and with nice syntax? type name literal int..int (range of int) 1..5 int..double (range of int to double) 1..5.0 int..int:int (stepped range) 5..1:-1 (I'm not sure of the use of mixed-type ranges, but this seems the most intuitive syntax. Since most ranges are probably of one type, how about allowing a symbol to denote "same type again". Any of the following could mean int..int: int..#, int.._, int..$)

I don't think it make sense to have mixed type ranges. The normal promotion rules should apply. However... Floating-point ranges are tricky. Should they be open-ended, or closed-ended?

Both Matlab and Numpy have floating point ranges. Matlab ranges are always inclusive, so 1:2.1:7.3 gives you 1.0, 3.1, 5.2, 7.3. Python ranges are always non-inclusive, so it gives you 1.0,3.1,5.2.
 Consider
 -real.infinity..real.infinity
 Are the infinities part of the range? If not, how do you specify a 
 range which includes infinity?

Does it matter that much? I suppose it would be cool if it did something really consistent, but Numpy just craps out and gives you an empty list, and Matlab raises an error "Maximum variable size allowed by the program is exceeded".

I think that if you can't specify a range including an infinity, then floating point ranges don't make sense. Especially, I really don't like the idea that -real.infinity..real.infinity would include -infinity, but not +infinity. I've had a use for floating-point ranges: specifying domain and range of functions, where infinity is fairly common. When else would you use them? Besides, "first_element .. last_element-1" doesn't work for (say) 0.00001 .. 0.00003; it has to be first_element..nextDown(lastElement). The MatLab method (closed ranges) is a nicer fit to IEEE arithmetic. In fact, I'd even say that half-open ranges are only ideal for unsigned numbers. But we probably don't want 1.0..5.0 to contain 5.0 when 1..5 doesn't contain 5.
Jul 23 2007
next sibling parent reply Sean Kelly <sean f4.ca> writes:
Don Clugston wrote:
 Bill Baxter wrote:
 Don Clugston wrote:

 Consider
 -real.infinity..real.infinity
 Are the infinities part of the range? If not, how do you specify a 
 range which includes infinity?

Does it matter that much? I suppose it would be cool if it did something really consistent, but Numpy just craps out and gives you an empty list, and Matlab raises an error "Maximum variable size allowed by the program is exceeded".

I think that if you can't specify a range including an infinity, then floating point ranges don't make sense. Especially, I really don't like the idea that -real.infinity..real.infinity would include -infinity, but not +infinity.

Hm... what if I wanted a range that included ulong.max? Is there any way to do that either? I don't suppose ulong.max+1 works in that case? I know it would be a tad weird because infinity+1 == infinity, but perhaps this is one case where the semantics should just be consistent with everything else. Sean
Jul 23 2007
parent reply Don Clugston <dac nospam.com.au> writes:
Sean Kelly wrote:
 Don Clugston wrote:
 Bill Baxter wrote:
 Don Clugston wrote:

 Consider
 -real.infinity..real.infinity
 Are the infinities part of the range? If not, how do you specify a 
 range which includes infinity?

Does it matter that much? I suppose it would be cool if it did something really consistent, but Numpy just craps out and gives you an empty list, and Matlab raises an error "Maximum variable size allowed by the program is exceeded".

I think that if you can't specify a range including an infinity, then floating point ranges don't make sense. Especially, I really don't like the idea that -real.infinity..real.infinity would include -infinity, but not +infinity.

Hm... what if I wanted a range that included ulong.max? Is there any way to do that either?

Probably not. The [a..b) definition of a range is great as long as you only use ranges for array slicing, but it doesn't generalise well to other use cases. To say x must be between -5.0 and +5.0, inclusive (mathematically [-5.0, 5.0]), using the existing semantics, you'd have to say: if (x in -5.0 .. nextUp(5.0)) ... and -5.0 to 5.0 exclusive (mathematically (-5.0, 5.0)) is: if (x in nextUp(-5.0) .. 5.0) ... Both of these cases are going to be far more common than [-5.0, 5.0) which should be as common as (-5.0, 5.0] which requires the monstrosity: if (x in nextUp(-5.0)..nextDown(5.0)) ... (and nextUp isn't even in Phobos - you have to use Tango <g>). I don't suppose ulong.max+1 works in that case? No.
   I know it would be a tad weird because infinity+1 == infinity, but 
 perhaps this is one case where the semantics should just be consistent 
 with everything else.

How can you store infinity + 1? Also, it won't work for 0.0001 .. 0.0003. You don't actually want to add 1.
Jul 23 2007
parent Sean Kelly <sean f4.ca> writes:
Don Clugston wrote:
 Sean Kelly wrote:
 Don Clugston wrote:
 Bill Baxter wrote:
 Don Clugston wrote:

 Consider
 -real.infinity..real.infinity
 Are the infinities part of the range? If not, how do you specify a 
 range which includes infinity?

Does it matter that much? I suppose it would be cool if it did something really consistent, but Numpy just craps out and gives you an empty list, and Matlab raises an error "Maximum variable size allowed by the program is exceeded".

I think that if you can't specify a range including an infinity, then floating point ranges don't make sense. Especially, I really don't like the idea that -real.infinity..real.infinity would include -infinity, but not +infinity.

Hm... what if I wanted a range that included ulong.max? Is there any way to do that either?

Probably not. The [a..b) definition of a range is great as long as you only use ranges for array slicing, but it doesn't generalise well to other use cases. To say x must be between -5.0 and +5.0, inclusive (mathematically [-5.0, 5.0]), using the existing semantics, you'd have to say: if (x in -5.0 .. nextUp(5.0)) ... and -5.0 to 5.0 exclusive (mathematically (-5.0, 5.0)) is: if (x in nextUp(-5.0) .. 5.0) ... Both of these cases are going to be far more common than [-5.0, 5.0) which should be as common as (-5.0, 5.0] which requires the monstrosity: if (x in nextUp(-5.0)..nextDown(5.0)) ...

Makes me feel like we were better off without foreachable ranges in the first place. It's obviously possible to do: foreach( f; inclusive( -float.infinity, float.infinity ) ) {} And it is potentially more meaningful as well, given that we can't use the mathematical notation [] vs [), etc. Also, just like the new foreachable ranges, the above syntax evaluates both the begin and end arguments only once and doesn't require the user to explicitly specify a type.
 (and nextUp isn't even in Phobos - you have to use Tango <g>).
 
   I don't suppose ulong.max+1 works in that case?
 No.
   I know it would be a tad weird because infinity+1 == infinity, but 
 perhaps this is one case where the semantics should just be consistent 
 with everything else.

How can you store infinity + 1?

You can't :-) For some reason I thought it would overflow to infinity and "just work", but you're right. The value has to be stored.
 Also, it won't work for 0.0001 .. 0.0003. You don't actually want to add 1.

Yup. Personally, I'd much rather have a separate, explicitly defined range syntax than this new foreach feature, or just leave things as-is. But then I'm not terribly fond of basically any new features introduced in 2.0, so I suppose this is just par for the course. Sean
Jul 23 2007
prev sibling parent reply Bill Baxter <dnewsgroup billbaxter.com> writes:
Don Clugston wrote:
 Bill Baxter wrote:
 Don Clugston wrote:
 Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free. What's wrong with adding that to the language, but templated and with nice syntax? type name literal int..int (range of int) 1..5 int..double (range of int to double) 1..5.0 int..int:int (stepped range) 5..1:-1 (I'm not sure of the use of mixed-type ranges, but this seems the most intuitive syntax. Since most ranges are probably of one type, how about allowing a symbol to denote "same type again". Any of the following could mean int..int: int..#, int.._, int..$)

I don't think it make sense to have mixed type ranges. The normal promotion rules should apply. However... Floating-point ranges are tricky. Should they be open-ended, or closed-ended?

Both Matlab and Numpy have floating point ranges. Matlab ranges are always inclusive, so 1:2.1:7.3 gives you 1.0, 3.1, 5.2, 7.3. Python ranges are always non-inclusive, so it gives you 1.0,3.1,5.2.
 Consider
 -real.infinity..real.infinity
 Are the infinities part of the range? If not, how do you specify a 
 range which includes infinity?

Does it matter that much? I suppose it would be cool if it did something really consistent, but Numpy just craps out and gives you an empty list, and Matlab raises an error "Maximum variable size allowed by the program is exceeded".

I think that if you can't specify a range including an infinity, then floating point ranges don't make sense. Especially, I really don't like the idea that -real.infinity..real.infinity would include -infinity, but not +infinity. I've had a use for floating-point ranges: specifying domain and range of functions, where infinity is fairly common. When else would you use them?

It sounds like maybe you're talking about "intervals" rather than "ranges". Yes, definitely intervals should be able to handle infinities correctly. But a range (a la python or matlab) is a shortcut for a sequence of values, with equal-size steps in between beginning and end. To have the beginning or end be infinite is asking for trouble. For instance in Matlab that tries to allocate an infinite-sized array of numbers.
 Besides, "first_element .. last_element-1" doesn't work for (say)
 0.00001 .. 0.00003;

Sure it does. It's just a set containing only 0.00001. I don't know what you mean by -1 there. Just think of it as a do-while loop that generates numbers: begin..end:step basically generates this: float[] a; float v=begin; do { a ~= v; v+=step; } while(v<end);
 it has to be first_element..nextDown(lastElement).
 The MatLab method (closed ranges) is a nicer fit to IEEE arithmetic.
 In fact, I'd even say that half-open ranges are only ideal for unsigned 
 numbers.
 
 But we probably don't want 1.0..5.0 to contain 5.0 when 1..5 doesn't 
 contain 5.

Right. Numpy had the same problem. Python itself uses the same non-inclusive rule as D. But Python only handles integers in things like the "range(start,end,step)" function. The Numpy folks wanted to extend that to work for floating point types as well. But actually, in both matlab and numpy, if you want an evenly spaced set of numbers, you usually use the 'linspace' function, which has the signature linspace(begin,end,numvals). This creates an inclusive array of numbers. I think one source of confusion is that ranges and slices are very similar things, but not quite the same. * A range is just a sequence of numbers. It can exist and be interpreted independently. Here allowing floating point numbers makes sense. Allowing for infinity may make sense, but practically it's very niche. Iterating over infinite things usually takes either too much time or too much memory. * A slice needs an object to operate on for interpretation of object-relative things like $. Generally speaking, only integers make sense in a slice. Infinity doesn't really make sense because you can't generally have things that are both slice-able and infinite on a computer. (* An interval just represents two points on a numberline, plus maybe an indication of the inclusivity of the endpoints. Infinity -- ok. Floating point -- ok.) It may be possible to combine the concepts into one type, but they *are* slightly different, and may benefit from being treated as so. --bb
Jul 23 2007
parent reply Don Clugston <dac nospam.com.au> writes:
Bill Baxter wrote:
 Don Clugston wrote:
 Bill Baxter wrote:
 Don Clugston wrote:
 Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free. What's wrong with adding that to the language, but templated and with nice syntax? type name literal int..int (range of int) 1..5 int..double (range of int to double) 1..5.0 int..int:int (stepped range) 5..1:-1 (I'm not sure of the use of mixed-type ranges, but this seems the most intuitive syntax. Since most ranges are probably of one type, how about allowing a symbol to denote "same type again". Any of the following could mean int..int: int..#, int.._, int..$)

I don't think it make sense to have mixed type ranges. The normal promotion rules should apply. However... Floating-point ranges are tricky. Should they be open-ended, or closed-ended?

Both Matlab and Numpy have floating point ranges. Matlab ranges are always inclusive, so 1:2.1:7.3 gives you 1.0, 3.1, 5.2, 7.3. Python ranges are always non-inclusive, so it gives you 1.0,3.1,5.2.
 Consider
 -real.infinity..real.infinity
 Are the infinities part of the range? If not, how do you specify a 
 range which includes infinity?

Does it matter that much? I suppose it would be cool if it did something really consistent, but Numpy just craps out and gives you an empty list, and Matlab raises an error "Maximum variable size allowed by the program is exceeded".

I think that if you can't specify a range including an infinity, then floating point ranges don't make sense. Especially, I really don't like the idea that -real.infinity..real.infinity would include -infinity, but not +infinity.

> functions, where infinity is fairly common. When else would you use them? > It sounds like maybe you're talking about "intervals" rather than "ranges". Yes, definitely intervals should be able to handle infinities correctly. But a range (a la python or matlab) is a shortcut for a sequence of values, with equal-size steps in between beginning and end.

OK, that makes sense. Although, for the integer case it's clear how many elements are in a range; it's not at all obvious for floating point.
  To have the beginning or end be infinite is asking for trouble.  For 
 instance in Matlab that tries to allocate an infinite-sized array of 
 numbers.

Agreed. Although 0..infinity is only one element bigger than 0..real.max.
 
 Besides, "first_element .. last_element-1" doesn't work for (say)
 0.00001 .. 0.00003;

Sure it does. It's just a set containing only 0.00001. I don't know what you mean by -1 there.

I mean, in the floating point case, you can't work out the last element of the range by subtracting 1 from it.
 But we probably don't want 1.0..5.0 to contain 5.0 when 1..5 doesn't 
 contain 5.

Right. Numpy had the same problem. Python itself uses the same non-inclusive rule as D. But Python only handles integers in things like the "range(start,end,step)" function. The Numpy folks wanted to extend that to work for floating point types as well. But actually, in both matlab and numpy, if you want an evenly spaced set of numbers, you usually use the 'linspace' function, which has the signature linspace(begin,end,numvals). This creates an inclusive array of numbers.

That makes sense. You could also have a logarithmic range. But what need is there for using ".." with floating point numbers? Surely we can already write foreach(float x, linspace(begin, end, numvals)){}
 I think one source of confusion is that ranges and slices are very 
 similar things, but not quite the same.
 
 * A range is just a sequence of numbers.  It can exist and be 
 interpreted independently.  Here allowing floating point numbers makes 
 sense.  Allowing for infinity may make sense, but practically it's very 
 niche.  Iterating over infinite things usually takes either too much 
 time or too much memory.

How is that different to a set? I've always assumed a range (a,b) contained EVERYTHING between a and b. I'm not very familiar with either Python or Matlab.
 * A slice needs an object to operate on for interpretation of 
 object-relative things like $.  Generally speaking, only integers make 
 sense in a slice.  Infinity doesn't really make sense because you can't 
 generally have things that are both slice-able and infinite on a computer.
 
 (* An interval just represents two points on a numberline, plus maybe an 
 indication of the inclusivity of the endpoints.  Infinity -- ok. 
 Floating point -- ok.)
 
 It may be possible to combine the concepts into one type, but they *are* 
 slightly different, and may benefit from being treated as so.

That clarification is very helpful. Thanks.
Jul 24 2007
parent Bill Baxter <dnewsgroup billbaxter.com> writes:
Don Clugston wrote:

 OK, that makes sense. Although, for the integer case it's clear how many 
 elements are in a range; it's not at all obvious for floating point.
 
  To have the beginning or end be infinite is asking for trouble.  For 
 instance in Matlab that tries to allocate an infinite-sized array of 
 numbers.

Agreed. Although 0..infinity is only one element bigger than 0..real.max.

Either way, it's still going to be a memory error in Matlab. The real.max one would probably be a memory error in Numpy too.
 Right.  Numpy had the same problem.  Python itself uses the same 
 non-inclusive rule as D. But Python only handles integers in things 
 like the "range(start,end,step)" function.  The Numpy folks wanted to 
 extend that to work for floating point types as well.  But actually, 
 in both matlab and numpy, if you want an evenly spaced set of numbers, 
 you usually use the 'linspace' function, which has the signature 
 linspace(begin,end,numvals).  This creates an inclusive array of numbers.

That makes sense. You could also have a logarithmic range.

Yes, both have a "logspace" function as well.
 But what need is there for using ".." with floating point numbers? 
 Surely we can already write
 foreach(float x, linspace(begin, end, numvals)){}

I can't really think of any super duper reason. It's just a shortcut for: for(float x=0.0; x<end; x+=0.1) { } I've used it in Python before. I think I used it more in Matlab, though, where the ranges are inclusive.
 I think one source of confusion is that ranges and slices are very 
 similar things, but not quite the same.

 * A range is just a sequence of numbers.  It can exist and be 
 interpreted independently.  Here allowing floating point numbers makes 
 sense.  Allowing for infinity may make sense, but practically it's 
 very niche.  Iterating over infinite things usually takes either too 
 much time or too much memory.

How is that different to a set? I've always assumed a range (a,b) contained EVERYTHING between a and b. I'm not very familiar with either Python or Matlab.

Yes. It is just a set. An ordered set with fixed spacing between elements, expressed using a compact notation.
 * A slice needs an object to operate on for interpretation of 
 object-relative things like $.  Generally speaking, only integers make 
 sense in a slice.  Infinity doesn't really make sense because you 
 can't generally have things that are both slice-able and infinite on a 
 computer.

 (* An interval just represents two points on a numberline, plus maybe 
 an indication of the inclusivity of the endpoints.  Infinity -- ok. 
 Floating point -- ok.)

 It may be possible to combine the concepts into one type, but they 
 *are* slightly different, and may benefit from being treated as so.

That clarification is very helpful. Thanks.

--bb
Jul 24 2007
prev sibling next sibling parent reply Bill Baxter <dnewsgroup billbaxter.com> writes:
Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free.

Thanks. I think Oskar Linde had a nice version too. I seem to remember thinking there were a few things in his that I should borrow.
 What's wrong with adding that to the language, but templated and with 
 nice syntax?
 
 type name                                 literal
 int..int  (range of int)                  1..5
 int..double   (range of int to double)    1..5.0
 int..int:int  (stepped range)             5..1:-1
 
 (I'm not sure of the use of mixed-type ranges, but this seems the most 
 intuitive syntax. Since most ranges are probably of one type, how about 
 allowing a symbol to denote "same type again". Any of the following 
 could mean int..int:   int..#,   int.._, int..$)

Having two different types for it seems odd. Just plain int.. would make more sense to me. I really like that 5..1:-1 syntax though! Was that mentioned before? Something about all the colons in Pythons range literals always makes me uneasy. a:b:c -- is that a to c stepping by b? Or a to b stepping by c? In Python it's the latter. In Matlab I think it's the former. Which is probably why I always feel a little uneasy when I see it. But a..b:c is much clearer! Obviously it's from a to b, so c must be a step. And the colon looking like the two dots stood on end -- lovely.
 As several people have pointed out, this also fixes mixed 
 indexing/slicing problems for multi-dimensional arrays.

To give Walter the benefit of the doubt, perhaps this new addition *is* the first stage of just such a master plan to make range literals first class citizens. --bb
Jul 23 2007
next sibling parent Reiner Pope <some address.com> writes:
Bill Baxter wrote:
 Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free.

Thanks. I think Oskar Linde had a nice version too. I seem to remember thinking there were a few things in his that I should borrow.
 What's wrong with adding that to the language, but templated and with 
 nice syntax?

 type name                                 literal
 int..int  (range of int)                  1..5
 int..double   (range of int to double)    1..5.0
 int..int:int  (stepped range)             5..1:-1

 (I'm not sure of the use of mixed-type ranges, but this seems the most 
 intuitive syntax. Since most ranges are probably of one type, how 
 about allowing a symbol to denote "same type again". Any of the 
 following could mean int..int:   int..#,   int.._, int..$)

Having two different types for it seems odd. Just plain int.. would make more sense to me. I really like that 5..1:-1 syntax though! Was that mentioned before? Something about all the colons in Pythons range literals always makes me uneasy. a:b:c -- is that a to c stepping by b? Or a to b stepping by c? In Python it's the latter. In Matlab I think it's the former. Which is probably why I always feel a little uneasy when I see it. But a..b:c is much clearer! Obviously it's from a to b, so c must be a step. And the colon looking like the two dots stood on end -- lovely.

I never knew about the Python or Matlab syntax. 5..1:-1 is from Norbert Nemec's multidimensional array proposal, and it makes so much sense. :) But I don't know about the declaration syntax of the type. The most obvious and the nicest-looking is definitely 'int..int'. But using that suggests that 'int..double' should be allowed, which doesn't really make much sense, given that operations on ranges will probably be mostly indexing, iterating through the range, and testing whether an element is contained in that range, each of which require one characteristic type. So the characteristic type of the range should only be said once. But I don't like int.. because of what it implies: int..: int: // a stepped range from here to infinity; but it looks like case: ..int: // I dunno: reverse iteration? You really need something to hold the number's place, But nothing comes to mind, other than (the ugly) # int..# int..#:# ..int:# Mind you, I think it allows a nice syntax for what I was grasping in a different post with the wacky question-mark syntax (int..int:int?). You need to be able to specify which promotions may be done implicitly, and with what default values. I think the easiest way is to specify the default values as part of the type: int..#:1 (a range from lo to hi, with step 1 unless specified) int..5:# int=3..# (lo has a default value of 3) One range, A, could only be implicitly converted to another if it every field in A was included in B (so we don't lose information) and all the fields in B missing from A have default values (so it's not implicitly converted by mistake). Just my train of thought, Reiner
Jul 23 2007
prev sibling parent renoX <renosky free.fr> writes:
Bill Baxter a écrit :
  I really like that 5..1:-1 syntax though!  Was 
 that mentioned before?  Something about all the colons in Pythons range 
 literals always makes me uneasy.  a:b:c -- is that a to c stepping by b? 
  Or a to b stepping by c?  In Python it's the latter.  In Matlab I think 
 it's the former.  Which is probably why I always feel a little uneasy 
 when I see it.  But a..b:c is much clearer!  Obviously it's from a to b, 
 so c must be a step.  And the colon looking like the two dots stood on 
 end -- lovely.

Lovely, yes, that's the first time I see this syntax, it's nice, but I wonder if the 'step' part is so important that sugar syntax is needed for it. In Ruby, they do the step part without sugar: 1..n.step(<step value>), the <step value> being optional with a default value of 1 (following a proposal of mine where they only took this part which was for me the least interesting point of the proposal *sigh*) IMHO, it'd better to concentrate on the range syntax and to get a nice one for all the cases: closed range, open, half-open. At one point I came with [<, [>, >], <] it's not very pretty but it's quite intuitive (at least for those who are used to math range, I bet that you guys can figure what means [<1, 5<] without I need to give explanations) it has a good visual effect I think and that contrary to just .. and ... it allows all the possibilities.. Regards, renoX
Jul 23 2007
prev sibling parent reply Reiner Pope <some address.com> writes:
Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free. What's wrong with adding that to the language, but templated and with nice syntax? type name literal int..int (range of int) 1..5 int..double (range of int to double) 1..5.0 int..int:int (stepped range) 5..1:-1 (I'm not sure of the use of mixed-type ranges, but this seems the most intuitive syntax. Since most ranges are probably of one type, how about allowing a symbol to denote "same type again". Any of the following could mean int..int: int..#, int.._, int..$) As several people have pointed out, this also fixes mixed indexing/slicing problems for multi-dimensional arrays. Reiner

Adding a '?' after the type means it's optional. This means two things: you can omit the value in literals, and it will be its default value; and it can be cast to from other range types, so 'int..int' can be implicitly converted to 'int..int:int?' but not 'int..int:int'. This gives a use for mixed-type ranges: typedef size_t step = 1; struct MyArray(T) { ... // returns a slice of the array, with a step of 1 unless specified MyArray!(T) opIndex(size_t..size_t:step? range) { ... } } But with # *and* ? being used by slice syntax, it might be using a few too many symbols for one concept.... Reiner
Jul 23 2007
parent Bill Baxter <dnewsgroup billbaxter.com> writes:
Reiner Pope wrote:
 Reiner Pope wrote:
 Bill Baxter wrote:
 Jarrett Billingsley wrote:
 "Xinok" <xnknet gmail.com> wrote in message 
 news:f80qof$2n0l$1 digitalmars.com...

 foreach(i; 0..100)

This is almost identical to the syntax in MiniD: for(i: 0 .. 100) It could be done with for or foreach; I just chose for because normally you use for loops to iterate over ranges of integers. You can also come up with a pretty simple short-term solution that'll be fairly efficient (though not as efficient as if the compiler were aware of this kind of loop intrinsically) by making a struct 'range' which has a static opCall to construct a range and an opApply to iterate over the values, so that it'd look like: foreach(i; range(100)) Which isn't terrible at all.

And it has the advantage of being more extensible. And for allowing ranges to be treated as first class entities that can be passed around and manipulated. But no, instead we get another one-trick pony. --bb

In the "Array Slice Ranges" thread, several people mentioned first-class ranges: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43865 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43904 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43905 http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digita mars.D&artnum=43954 Your implementation, Bill, seems to be just right, and gives you foreach over ranges for free. What's wrong with adding that to the language, but templated and with nice syntax? type name literal int..int (range of int) 1..5 int..double (range of int to double) 1..5.0 int..int:int (stepped range) 5..1:-1 (I'm not sure of the use of mixed-type ranges, but this seems the most intuitive syntax. Since most ranges are probably of one type, how about allowing a symbol to denote "same type again". Any of the following could mean int..int: int..#, int.._, int..$) As several people have pointed out, this also fixes mixed indexing/slicing problems for multi-dimensional arrays. Reiner

Adding a '?' after the type means it's optional. This means two things: you can omit the value in literals, and it will be its default value; and it can be cast to from other range types, so 'int..int' can be implicitly converted to 'int..int:int?' but not 'int..int:int'. This gives a use for mixed-type ranges: typedef size_t step = 1; struct MyArray(T) { ... // returns a slice of the array, with a step of 1 unless specified MyArray!(T) opIndex(size_t..size_t:step? range) { ... } } But with # *and* ? being used by slice syntax, it might be using a few too many symbols for one concept....

Let's just call it __slice. I think __traits is lonely. --bb
Jul 23 2007