http://d.puremagic.com/issues/show_bug.cgi?id=3235

           Summary: Function literals must be deduced as "function" or
                    "delegate"
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: andrei@metalanguage.com


Consider:

void foo(alias pred)() {
    pragma(msg, pred.stringof);
}

unittest {
    foo!((i) { return i < 0; })();
    int z = 1;
    foo!((i) { return i < z; })();
}

void main(string[] args)
{
}

This outputs:

__funcliteral1(__T2)
__dgliteral3(__T4)

because the first literal does not have to be a delegate.

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--- Comment #1 from Andrei Alexandrescu <andrei@metalanguage.com>  2009-08-08 07:17:17 PDT ---
(In reply to comment #0)
> Consider:
> 
> void foo(alias pred)() {
>     pragma(msg, pred.stringof);
> }
> 
> unittest {
>     foo!((i) { return i < 0; })();
>     int z = 1;
>     foo!((i) { return i < z; })();
> }
> 
> void main(string[] args)
> {
> }
> 
> This outputs:
> 
> __funcliteral1(__T2)
> __dgliteral3(__T4)
> 
> because the first literal does not have to be a delegate.

I meant that right now this outputs:

__dgliteral1(__T2)
__dgliteral3(__T4)

and it should output:

__funcliteral1(__T2)
__dgliteral3(__T4)

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Stewart Gordon <smjg@iname.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |smjg@iname.com
         Resolution|                            |INVALID




--- Comment #2 from Stewart Gordon <smjg@iname.com>  2009-08-08 11:14:14 PDT ---
This is as designed.

http://www.digitalmars.com/d/1.0/expression.html#FunctionLiteral
"If the keywords function or delegate are omitted, it defaults to being a
delegate."

Having the type of a function/delegate literal depend on its contents like this makes it hard for someone reading the code to tell which it is.  Since function pointers and delegates are not generally interchangeable, AISI it's desirable to keep their literal notations distinct.

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--- Comment #3 from Andrei Alexandrescu <andrei@metalanguage.com>  2009-08-08 11:55:19 PDT ---
(In reply to comment #2)
> This is as designed.
> 
> http://www.digitalmars.com/d/1.0/expression.html#FunctionLiteral
> "If the keywords function or delegate are omitted, it defaults to being a
> delegate."
> 
> Having the type of a function/delegate literal depend on its contents like this makes it hard for someone reading the code to tell which it is.  Since function pointers and delegates are not generally interchangeable, AISI it's desirable to keep their literal notations distinct.

I think type deduction should help here as much as anywhere else. If you do want a delegate, you can always use the delegate keyword. Plus, all algorithms in std.algorithm take an efficiency toll when used with literals.

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Andrei Alexandrescu <andrei@metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |




--- Comment #4 from Andrei Alexandrescu <andrei@metalanguage.com>  2009-08-08 11:57:05 PDT ---
(In reply to comment #2)
> This is as designed.
> 
> http://www.digitalmars.com/d/1.0/expression.html#FunctionLiteral
> "If the keywords function or delegate are omitted, it defaults to being a
> delegate."
> 
> Having the type of a function/delegate literal depend on its contents like this makes it hard for someone reading the code to tell which it is.  Since function pointers and delegates are not generally interchangeable, AISI it's desirable to keep their literal notations distinct.

I think type deduction should help here as much as anywhere else. If you do want a delegate, you can always use the delegate keyword. Plus, all algorithms in std.algorithm take an efficiency toll when used with literals.

(Please do not mark this as resolved; I've discussed with Walter before posting it, and he suggested I do. In general, the spec of D2 is fluid enough to not be a strong reason for invalidating a bug report. Thanks.)

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--- Comment #5 from Andrei Alexandrescu <andrei@metalanguage.com> 2011-04-28 13:39:40 PDT ---
BTW this is in TDPL now, with Walter's approval.

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Andrei Alexandrescu <andrei@metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|TDPL: Function literals     |[tdpl] Function literals
                   |must be deduced as          |must be deduced as
                   |"function" or "delegate"    |"function" or "delegate"


--- Comment #6 from Andrei Alexandrescu <andrei@metalanguage.com> 2011-12-18 20:05:41 PST ---
The following example is in TDPL:

unittest
{
  auto f = (int i) {};
  assert(is(f == function));
}

The example fails to compile (it should). Also the following example should
work:

unittest
{
  int a;
  auto f = (int i) { a = i; };
  assert(is(f == delegate));
}

The compiler should automatically infer function or delegate type depending on the literal's use of local state. The argument against it - people change a detail in the body of the function and its type changes - is non sequitur. Changing a literal from 10 to 10.0 also changes its type. Please fix.

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Kenji Hara <k.hara.pg@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


--- Comment #7 from Kenji Hara <k.hara.pg@gmail.com> 2011-12-30 21:23:43 PST ---
https://github.com/D-Programming-Language/dmd/pull/588

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
                 CC|                            |bugzilla@digitalmars.com
         Resolution|                            |FIXED


--- Comment #8 from Walter Bright <bugzilla@digitalmars.com> 2011-12-31 12:22:38 PST ---
https://github.com/D-Programming-Language/dmd/commit/c50eb5f5726a65efa1224ff0f0fd60acbb6e3027

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