digitalmars.D - is this considered inconsistency?

mw (18/18) Mar 21 2021 https://run.dlang.io/is/VOGlGN

Steven Schveighoffer (3/26) Mar 21 2021 That would be the least useful behavior.

mw (5/32) Mar 21 2021 It's useful (to be consistent): it reduces user's burden to write

Dennis (13/15) Mar 21 2021 In `foreach (i; 0 .. -1)`, `i` is typed `int`. In a slice, the

mw (4/14) Mar 21 2021 Indeed, this shouldn't be allowed, bite by this a number of

Paul Backus (4/9) Mar 21 2021 There have been proposals to change the integer promotion rules

mw (13/23) Mar 21 2021 "compatible with C" as a goal of D?

mw (3/28) Mar 21 2021 Typo:

Imperatorn (5/29) Mar 23 2021 It would probably have to be the other way around though. Begin

mw <mingwu gmail.com> writes:

https://run.dlang.io/is/VOGlGN

void main()
{
     import std.stdio: writeln;
     {
         // example from "Introduction to Algorithms" Cormen et 
al., p 146
         int[] a = [ 4, 1, 3, 2, 16, 9, 10, 14, 8, 7 ];

         foreach (i;   0 ..  1 ) writeln(i);  // 0
         foreach (i;   0 ..  0 ) writeln(i);  // no output
         foreach (i;   0 .. -1 ) writeln(i);  // no output

         foreach (i; a[0 ..  1]) writeln(i);  // 4
         foreach (i; a[0 ..  0]) writeln(i);  // no output
         foreach (i; a[0 .. -1]) writeln(i);  // Range violation
     }
}

Why can't the a[0 .. -1] just return empty range, when end <= 
start, as in a[0 ..  0]? and also in foreach (i;   0 .. -1 )?

Mar 21 2021

Steven Schveighoffer <schveiguy gmail.com> writes:

On 3/21/21 11:55 AM, mw wrote:
 https://run.dlang.io/is/VOGlGN
 
 void main()
 {
      import std.stdio: writeln;
      {
          // example from "Introduction to Algorithms" Cormen et al., p
146
          int[] a = [ 4, 1, 3, 2, 16, 9, 10, 14, 8, 7 ];
 
          foreach (i;   0 ..  1 ) writeln(i);  // 0
          foreach (i;   0 ..  0 ) writeln(i);  // no output
          foreach (i;   0 .. -1 ) writeln(i);  // no output
 
          foreach (i; a[0 ..  1]) writeln(i);  // 4
          foreach (i; a[0 ..  0]) writeln(i);  // no output
          foreach (i; a[0 .. -1]) writeln(i);  // Range violation
      }
 }
 
 Why can't the a[0 .. -1] just return empty range, when end <= start, as 
 in a[0 ..  0]? and also in foreach (i;   0 .. -1 )?
 
 

That would be the least useful behavior.

-Steve

Mar 21 2021

mw <mingwu gmail.com> writes:

On Sunday, 21 March 2021 at 16:21:44 UTC, Steven Schveighoffer 
wrote:
 On 3/21/21 11:55 AM, mw wrote:
 https://run.dlang.io/is/VOGlGN
 
 void main()
 {
      import std.stdio: writeln;
      {
          // example from "Introduction to Algorithms" Cormen 
 et al., p 146
          int[] a = [ 4, 1, 3, 2, 16, 9, 10, 14, 8, 7 ];
 
          foreach (i;   0 ..  1 ) writeln(i);  // 0
          foreach (i;   0 ..  0 ) writeln(i);  // no output
          foreach (i;   0 .. -1 ) writeln(i);  // no output
 
          foreach (i; a[0 ..  1]) writeln(i);  // 4
          foreach (i; a[0 ..  0]) writeln(i);  // no output
          foreach (i; a[0 .. -1]) writeln(i);  // Range 
 violation
      }
 }
 
 Why can't the a[0 .. -1] just return empty range, when end <= 
 start, as in a[0 ..  0]? and also in foreach (i;   0 .. -1 )?
 
 

 That would be the least useful behavior.

It's useful (to be consistent): it reduces user's burden to write 
the bound check explicitly (verbosely), i.e foreach (i; a[0 .. 
max(0, end)]) {...}

Mar 21 2021

Dennis <dkorpel gmail.com> writes:

On Sunday, 21 March 2021 at 15:55:04 UTC, mw wrote:
 Why can't the a[0 .. -1] just return empty range, when end <= 
 start, as in a[0 ..  0]? and also in foreach (i;   0 .. -1 )?

In `foreach (i; 0 .. -1)`, `i` is typed `int`. In a slice, the 
indices are of type `size_t` which is an unsigned integer type. 
-1 underflows to `ulong.max` (on 64-bit) which is why you get a 
range violation.

You could define your own slice type as a struct with operator 
overloads, where you can use signed indices or automatic clamping 
of the bounds or whatever you want. Changing the behavior of the 
language type would be a breaking and possibly controversial 
change.

There's also a point to be made that the implicit conversion from 
signed to unsigned integers should not be allowed, that's a 
separate discussion.

Mar 21 2021

mw <mingwu gmail.com> writes:

On Sunday, 21 March 2021 at 16:47:41 UTC, Dennis wrote:
 On Sunday, 21 March 2021 at 15:55:04 UTC, mw wrote:
 Why can't the a[0 .. -1] just return empty range, when end <= 
 start, as in a[0 ..  0]? and also in foreach (i;   0 .. -1 )?

 In `foreach (i; 0 .. -1)`, `i` is typed `int`. In a slice, the 
 indices are of type `size_t` which is an unsigned integer type. 
 -1 underflows to `ulong.max` (on 64-bit) which is why you get a 
 range violation.

Ahh, This explains.

 There's also a point to be made that the implicit conversion 
 from signed to unsigned integers should not be allowed, that's 
 a separate discussion.

Indeed, this shouldn't be allowed, bite by this a number of 
times. Is there a DIP on this already?

Mar 21 2021

Paul Backus <snarwin gmail.com> writes:

On Sunday, 21 March 2021 at 17:01:27 UTC, mw wrote:
 There's also a point to be made that the implicit conversion 
 from signed to unsigned integers should not be allowed, that's 
 a separate discussion.

 Indeed, this shouldn't be allowed, bite by this a number of 
 times. Is there a DIP on this already?

There have been proposals to change the integer promotion rules 
in the past, but they've been rejected because Walter wants to 
keep them compatible with C, to make porting C code to D easier.

Mar 21 2021

mw <mingwu gmail.com> writes:

On Sunday, 21 March 2021 at 21:22:16 UTC, Paul Backus wrote:
 On Sunday, 21 March 2021 at 17:01:27 UTC, mw wrote:
 There's also a point to be made that the implicit conversion 
 from signed to unsigned integers should not be allowed, 
 that's a separate discussion.

 Indeed, this shouldn't be allowed, bite by this a number of 
 times. Is there a DIP on this already?

 There have been proposals to change the integer promotion rules 
 in the past, but they've been rejected because Walter wants to 
 keep them compatible with C, to make porting C code to D easier.

"compatible with C" as a goal of D?

Then why we need D? C++ has been there already 😎


Instead of let a few people decide, how about also let the users 
decide?

I have read -dipxxx switches are kind of previews (not formally 
in to the language).

How about add a -dip-no-explicit-conversion preview, but ask the 
users permission to send their actuall complier build flags (of 
their daily work) back to dlang.org, and let that statistics be 
part of the decision factor?

E.g, if 99.999% of the users always have that flag turned on, why 
not have that feature into the language?

Mar 21 2021

mw <mingwu gmail.com> writes:

On Sunday, 21 March 2021 at 22:56:43 UTC, mw wrote:
 On Sunday, 21 March 2021 at 21:22:16 UTC, Paul Backus wrote:
 On Sunday, 21 March 2021 at 17:01:27 UTC, mw wrote:
 There's also a point to be made that the implicit conversion 
 from signed to unsigned integers should not be allowed, 
 that's a separate discussion.

 Indeed, this shouldn't be allowed, bite by this a number of 
 times. Is there a DIP on this already?

 There have been proposals to change the integer promotion 
 rules in the past, but they've been rejected because Walter 
 wants to keep them compatible with C, to make porting C code 
 to D easier.

 "compatible with C" as a goal of D?

 Then why we need D? C++ has been there already 😎


 Instead of let a few people decide, how about also let the 
 users decide?

 I have read -dipxxx switches are kind of previews (not formally 
 in to the language).

 How about add a -dip-no-explicit-conversion preview, but ask 
 the users permission to send their actuall complier build flags 
 (of their daily work) back to dlang.org, and let that 
 statistics be part of the decision factor?

 E.g, if 99.999% of the users always have that flag turned on, 
 why not have that feature into the language?


Typo:
-dip-no-implicit-conversion

Mar 21 2021

Imperatorn <johan_forsberg_86 hotmail.com> writes:

On Sunday, 21 March 2021 at 22:59:26 UTC, mw wrote:
 On Sunday, 21 March 2021 at 22:56:43 UTC, mw wrote:
 On Sunday, 21 March 2021 at 21:22:16 UTC, Paul Backus wrote:
 [...]

 "compatible with C" as a goal of D?

 Then why we need D? C++ has been there already 😎


 Instead of let a few people decide, how about also let the 
 users decide?

 I have read -dipxxx switches are kind of previews (not 
 formally in to the language).

 How about add a -dip-no-explicit-conversion preview, but ask 
 the users permission to send their actuall complier build 
 flags (of their daily work) back to dlang.org, and let that 
 statistics be part of the decision factor?

 E.g, if 99.999% of the users always have that flag turned on, 
 why not have that feature into the language?


 Typo:
 -dip-no-implicit-conversion

It would probably have to be the other way around though. Begin 
by having a --allow-implicit-conversion, then after x amount of 
time it could possibly be default. But this is a major thing so I 
doubt it

Mar 23 2021

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digitalmars.D - is this considered inconsistency?