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digitalmars.D - $, __dollar, opDollar: can't define my own?

reply "Chris Miller" <chris dprogramming.com> writes:
There should be an opDollar, or some other name, such as opEnd, to  
overload $ for user-defined classes/structs/unions. Or instead, it could  
even simply just access a length member if it exists.

I have a struct that wraps an array and works like an array in almost  
every way except for the $ feature of arrays.
Oct 03 2006
next sibling parent reply Oskar Linde <oskar.lindeREM OVEgmail.com> writes:
Chris Miller wrote:

 There should be an opDollar, or some other name, such as opEnd, to 
 overload $ for user-defined classes/structs/unions. Or instead, it could 
 even simply just access a length member if it exists.
 
 I have a struct that wraps an array and works like an array in almost 
 every way except for the $ feature of arrays.


It would also be very nice to support $ in some way for multidimensional 
indexing:

myclass[$-1, $-1]

myclass[1..$-1, x % $]

For some of my own classes, I have a templated opIndex that supports:

myclass[end-1,end-1]

myclass[range(1,end-1), x % end]

etc...

It would be really nice to get the same functionality with the first syntax.

My solution is to make special types. Briefly:

struct End {
   EndRel opMinus(int i) { EndRel x = {i}; return x; }
   EndMod opMod_r(int i) { EndMod x = {i}; return x; }
}

End end; // Global end instance

struct EndRel { int i; }
struct EndMod { int i; }

struct FullRange {}

Fullrange all; // Global all range

struct Range {
   int start, end;
}

struct EndRange {
   int start;
}

struct EndRelRange {
   int start;
   int endrel;
}

Range range(int start, int end) { Range x = {start,end}; return x; }

EndRange range(int start, End dummy) { EndRange x = {start}; return x; }

EndRelRange range(int start, EndRel endrel) {
   EndRelRange x = {start,endrel};
   return x;
}

The class template code for opIndex then need to handle arguments of 
types int, End, EndRel, EndMod, FullRange, Range, EndRange, EndRelRange, 
etc...

This may all be a bit overkill, but what would be really great is having 
a range type that a..b expands into at lest. That type could then 
support opApply making

foreach(i; 0..10) { ... }

possible for instance.

/Oskar
Oct 03 2006
next sibling parent "Andrey Khropov" <andkhropov_nosp m_mtu-net.ru> writes:
Oskar Linde wrote:


 This may all be a bit overkill, but what would be really great is having a
 range type that a..b expands into at lest. That type could then support
 opApply making
 
 foreach(i; 0..10) { ... }
 
 possible for instance.



Yes, I'm also curious why slices aren't first class objects in D: 
http://www.digitalmars.com/d/archives/40556.html.

It would be just so handy, especially if you do a lot of vector/matrix/tensor
operations. I just got sick and tired writing infinite

"for(int i = 0; i < n; ++i)" in my C++ code :(

-- 
AKhropov
Oct 04 2006
prev sibling parent Fredrik Olsson <peylow gmail.com> writes:
Oskar Linde skrev:
<snip>

 This may all be a bit overkill, but what would be really great is having 
 a range type that a..b expands into at lest. That type could then 
 support opApply making
 
 foreach(i; 0..10) { ... }
 
 possible for instance.
 


YES! Ranges and sets, as I have pleaded for ages. It is a bliss for 
reducing code size, and allows some very nice readability stuff. It is 
not that hard to implement either, most Pascal implementations does it 
with a simple bit-field.
Doing it with templates and tricks gets you the functionality, but 
misses the point of a clean and readable syntax.

// is it lowercase ASCII?
if (ch in 'a'..'z') { ... }

// Is the selection bold?
if (TextAttriibutes.BOLD in text.selection.attributes() { ... }

// Make selected text underline.
text.selection.attributes += TextAttriibutes.UNDERLINE;

// Get all days where both Adam and Beatrice are free, but not monday.
goodDays = adam.availableDays - beatrice.availableDays - Days.MONDAY;


Ranges and sets are priceless for handling "a bag of values", without 
the need to write error prone iterations, or just as error prone and 
large boolean expressions.


// Fredrik Olsson
Oct 04 2006
prev sibling parent "icee" <iceelyne gmail.com> writes:
 overload $ for user-defined classes/structs/unions. Or instead, it could 
 even simply just access a length member if it exists.


just take the place of .length, not a separate overload.
Oct 04 2006