digitalmars.D.learn - Filling a char array with letters and element type of char[]

Kadir Erdem Demir (26/26) Mar 03 2015 I have an char[];

Tobias Pankrath (8/16) Mar 03 2015 I have no time to dig into this, but:

Jonathan M Davis via Digitalmars-d-learn (3/23) Mar 03 2015 http://stackoverflow.com/questions/6401365
Steven Schveighoffer (14/25) Mar 03 2015 You cannot currently.

Jonathan M Davis via Digitalmars-d-learn (8/12) Mar 03 2015 I think that at this point, most of the core developers think that

Steven Schveighoffer (7/19) Mar 03 2015 Sure, but I think that for phobos to say you can't fill a large char[]

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (18/23) Mar 03 2015 std.string.representation works in this case.

Kadir Erdem Demir (5/5) Mar 04 2015 @Tobias @Ali @Jonathan @Steven

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (8/16) Mar 03 2015 .front of a char range is a dchar that is created on the fly (i.e. it is...

"Kadir Erdem Demir" <kerdemdemir hotmail.com> writes:

I have an char[];

char[] strArr = "http://www.hurriyet.com.tr/ekonomi".dup;

I stripped the domain out of url like:

auto domain = findSplitAfter(strArr, "http://")[1].until('/');

Than because I am new to the language I became curious if I 
change domain(which I believe a input iterator); the values of 
strArr will also change or not. I tried to to modify domain like :

fill(domain, 'a');

Which gives error :
"cannot deduce function from argument types !()(Until!("a == b", 
char[], char), char)"

But if the array is a array of ints it compiles. I believe it 
fails because in compile messages I see

std.algorithm.fill(Range, Value)(Range range, Value filler) if 
(isInputRange!Range && is(typeof(range.front = filler)))

and

writeln( is(typeof(url.front = 'a')) );  ---> false
writeln( is(typeof(intArr.front = 0)) ); ---> true(that is why 
compiles)

I have three questions?

If I change the iterator which I get from algorithm, the owner 
data will change or not?

How to use std.algorithm.fill with char types?

What is the type of char array holds why it does not matches char?

Regards
Kadir Erdem

Mar 03 2015

"Tobias Pankrath" <tobias pankrath.net> writes:

 I have three questions?

 If I change the iterator which I get from algorithm, the owner 
 data will change or not?

 How to use std.algorithm.fill with char types?

 What is the type of char array holds why it does not matches 
 char?

 Regards
 Kadir Erdem

I have no time to dig into this, but:

is(typeof(arr.front = 'a')) does _not_ check if arr.front is of 
type char. It is true if you can assign an 'a' to arr.front.

is(typeof(_expr_)) is another way to write __traits(compiles, 
_expr).

So, either the range returned by until has elements that are not 
assignable or the reason is that until returns a range of dchar, 
because all string types are treated as ranges of dchar.

Mar 03 2015

Jonathan M Davis via Digitalmars-d-learn writes:

On Tuesday, March 03, 2015 09:06:03 Tobias Pankrath via Digitalmars-d-learn
wrote:
 I have three questions?

 If I change the iterator which I get from algorithm, the owner
 data will change or not?

 How to use std.algorithm.fill with char types?

 What is the type of char array holds why it does not matches
 char?

 Regards
 Kadir Erdem

 I have no time to dig into this, but:

 is(typeof(arr.front = 'a')) does _not_ check if arr.front is of
 type char. It is true if you can assign an 'a' to arr.front.

 is(typeof(_expr_)) is another way to write __traits(compiles,
 _expr).

 So, either the range returned by until has elements that are not
 assignable or the reason is that until returns a range of dchar,
 because all string types are treated as ranges of dchar.

http://stackoverflow.com/questions/6401365

- Jonathan M Davis

Mar 03 2015

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 3/3/15 4:06 AM, Tobias Pankrath wrote:
 I have three questions?

 If I change the iterator which I get from algorithm, the owner data
 will change or not?


I'm not sure about this question.

 How to use std.algorithm.fill with char types?


You cannot currently.

 What is the type of char array holds why it does not matches char?


Because D is schizophrenic ;) Phobos considers char[] arrays not to be 
arrays of char, only ranges of dchar. Unless you talk to the compiler, 
where it happily treats char[] as an array.

 I have no time to dig into this, but:

 is(typeof(arr.front = 'a')) does _not_ check if arr.front is of type
 char. It is true if you can assign an 'a' to arr.front.

That is the check in std.algorithm. It wants to fill the array by 
assigning 'a' to the front. In D land, char[] arrays are ranges of 
dchars, and are only READABLE. This means a char[] array can never be an 
output range. Boatloads of code specializes char[] arrays in order to 
work around this.

I guess we need another specialization (because this should be allowed, 
IMO).

-Steve

Mar 03 2015

Jonathan M Davis via Digitalmars-d-learn writes:

On Tuesday, March 03, 2015 08:50:35 Steven Schveighoffer via
Digitalmars-d-learn wrote:
 What is the type of char array holds why it does not matches char?


 Because D is schizophrenic ;) Phobos considers char[] arrays not to be
 arrays of char, only ranges of dchar. Unless you talk to the compiler,
 where it happily treats char[] as an array.

I think that at this point, most of the core developers think that
auto-decoding was a mistake, but fixing it would definitely be a bit of a
mess, and whenever it comes up, Andrei complains that we need to focus on
other things and that we're blowing it out of proportion. :|

I think that the auto-decoding was well-intentioned and an interesting
experiment, but ultimately, it's causing too many problems...

- Jonathan M Davis

Mar 03 2015

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 3/3/15 2:32 PM, Jonathan M Davis via Digitalmars-d-learn wrote:
 On Tuesday, March 03, 2015 08:50:35 Steven Schveighoffer via
Digitalmars-d-learn wrote:
 What is the type of char array holds why it does not matches char?


 Because D is schizophrenic ;) Phobos considers char[] arrays not to be
 arrays of char, only ranges of dchar. Unless you talk to the compiler,
 where it happily treats char[] as an array.

 I think that at this point, most of the core developers think that
 auto-decoding was a mistake, but fixing it would definitely be a bit of a
 mess, and whenever it comes up, Andrei complains that we need to focus on
 other things and that we're blowing it out of proportion. :|

 I think that the auto-decoding was well-intentioned and an interesting
 experiment, but ultimately, it's causing too many problems...

Sure, but I think that for phobos to say you can't fill a large char[] 
with a repeat of small char[], but you can fill a large int[] with a 
repeat of small int[], is more of a problem than somehow fixing the 
underlying situation.

Other algorithms treat char[] specially. fill should too.

-Steve

Mar 03 2015

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 03/03/2015 11:38 AM, Steven Schveighoffer wrote:

 Sure, but I think that for phobos to say you can't fill a large char[]
 with a repeat of small char[], but you can fill a large int[] with a
 repeat of small int[], is more of a problem than somehow fixing the
 underlying situation.

 Other algorithms treat char[] specially. fill should too.

std.string.representation works in this case.

import std.stdio;
import std.algorithm;
import std.string;

void main()
{
     char[] strArr = "http://www.hurriyet.com.tr/ekonomi".dup;
     auto domain = findSplitAfter(strArr.representation,
                                  "http://")[1].until('/');
     fill(domain, 'a');
     writeln(strArr);
}

Prints

http://aaaaaaaaaaaaaaaaaaa/ekonomi

Ali

P.S. Grrr. Why can't I ever remember the name of that function! 
(representation, representation, representation, ...)

Mar 03 2015

"Kadir Erdem Demir" <kerdemdemir hotmail.com> writes:

 Tobias  Ali  Jonathan  Steven

Thanks alot for your answers.
I will try to learn as much as I can from them.

Regards
Erdem

Mar 04 2015

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 03/03/2015 12:18 AM, Kadir Erdem Demir wrote:

 I have an char[];

 char[] strArr = "http://www.hurriyet.com.tr/ekonomi".dup;

 I stripped the domain out of url like:

 auto domain = findSplitAfter(strArr, "http://")[1].until('/');

 Than because I am new to the language I became curious if I change
 domain(which I believe a input iterator); the values of strArr will also
 change or not.

.front of a char range is a dchar that is created on the fly (i.e. it is 
an rvalue), effectively making such ranges "generators". If possible, 
setting the returned dchar would not change the original char.

 But if the array is a array of ints it compiles.

Elements of some ranges (e.g. slices) are lvalues. When needed, 
hasLvalueElements can detect the kind of range at compile time:

   http://dlang.org/phobos/std_range.html#hasLvalueElements

Ali

Mar 03 2015

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digitalmars.D.learn - Filling a char array with letters and element type of char[]