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August 08, 2009
[Issue 3235] New: Function literals must be deduced as "function" or "delegate"
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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August 08, 2009
[Issue 3235] Function literals must be deduced as "function" or "delegate"
http://d.puremagic.com/issues/show_bug.cgi?id=3235





--- 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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August 08, 2009
[Issue 3235] Function literals must be deduced as "function" or "delegate"
http://d.puremagic.com/issues/show_bug.cgi?id=3235


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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[Issue 3235] Function literals must be deduced as "function" or "delegate"
http://d.puremagic.com/issues/show_bug.cgi?id=3235





--- 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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August 08, 2009
[Issue 3235] Function literals must be deduced as "function" or "delegate"
http://d.puremagic.com/issues/show_bug.cgi?id=3235


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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April 28, 2011
[Issue 3235] Function literals must be deduced as "function" or "delegate"
http://d.puremagic.com/issues/show_bug.cgi?id=3235



--- 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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December 19, 2011
[Issue 3235] [tdpl] Function literals must be deduced as "function" or "delegate"
http://d.puremagic.com/issues/show_bug.cgi?id=3235


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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December 31, 2011
[Issue 3235] [tdpl] Function literals must be deduced as "function" or "delegate"
http://d.puremagic.com/issues/show_bug.cgi?id=3235


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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December 31, 2011
[Issue 3235] [tdpl] Function literals must be deduced as "function" or "delegate"
http://d.puremagic.com/issues/show_bug.cgi?id=3235


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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