http://d.puremagic.com/issues/show_bug.cgi?id=3866

           Summary: anonymous delegate with default parameters cross-talks
                    to another anonymous  delegate
           Product: D
           Version: 2.040
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: philippe.sigaud@gmail.com


--- Comment #0 from Philippe Sigaud <philippe.sigaud@gmail.com> 2010-03-01 18:36:25 CET ---
If you declare an anonymous delegate with default parameter, it affects another anonymous delegate with the same type:

import std.stdio;
void main() {

    auto foo = (int a = 1) { return a;};
    auto bar = (int a) { return a;};

    writeln(foo()); // writes '1'
    writeln(bar()); // writes '1' also!
}

It provokes (correctly) an error if bar is defined before foo: bar() called
with 0 argument instead of 1.

It does not affect delegate with another type

    auto baz = (double a) { return a;};
    writeln(baz()); // Error, correct behaviour

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
                 CC|                            |clugdbug@yahoo.com.au
           Severity|normal                      |critical


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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
                 CC|                            |yebblies@gmail.com
           Platform|Other                       |All
         OS/Version|Windows                     |All


--- Comment #1 from yebblies <yebblies@gmail.com> 2011-07-03 23:14:23 EST ---
https://github.com/D-Programming-Language/dmd/pull/204

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|nobody@puremagic.com        |yebblies@gmail.com


--- Comment #2 from yebblies <yebblies@gmail.com> 2012-02-12 13:55:08 EST ---
The problem occurs because default parameters are stored in the type, but types are considered equivalent if their mangled names match, and mangled names don't include parameter names or default arguments.

The solution is probably either to include parameter names and default arguments in the comparison for equality, or to move them out of function types and into function declarations.  I'm leaning towards the latter.

This case _can_ be fixed by refusing to merge function pointers, but the problem will still exists for pointers to function pointers, structs containing function pointers, etc.

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla@digitalmars.com


--- Comment #3 from Walter Bright <bugzilla@digitalmars.com> 2012-04-25 20:35:30 PDT ---
Moving the default arguments out of the type and into the function declaration will resolve the problem, at the cost of you would no longer be able to have default arguments for function literals or any pointers to functions.

Perhaps that's a good thing.

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Jonathan M Davis <jmdavisProg@gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jmdavisProg@gmx.com


--- Comment #4 from Jonathan M Davis <jmdavisProg@gmx.com> 2012-04-26 10:33:19 PDT ---
It was my understanding that default arguments were just arguments that were inserted when a function was called and you didn't provide all of the arguments. They aren't actually part of the signature or type at all. As such, they are only known if you call the function directly. If you use a function pointer (or delegate), then all you have is the signature, so you don't have any default arguments. As such, nested functions with default arguments such as

static auto foo(int a = 1)
{
    return a;
}

and

auto foo(int a = 1)
{
    return a + b;
}

should work just fine, but as with any function, as soon as you take their address or turn them into a delegate variable, their default arguments are lost. And so having default arguments in something like

auto foo = (int a = 1) { return a;};
auto bar = (int a) { return a;};

is completely pointless, because all you have is a variable which knows the signature of the function/delegate to call. The function itself can't be called directly, so it doesn't have any default arguments associated with it, and so there's no point in the default arguments even being legal.

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--- Comment #5 from Walter Bright <bugzilla@digitalmars.com> 2012-04-26 23:06:52 PDT ---
Leaving this as-is for D1 to avoid breaking existing code.

For D2, changing behavior so that default args are part of the declaration, not the type, and so both function calls in the example are illegal, since calling through a function pointer now cannot have default args.

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--- Comment #6 from github-bugzilla@puremagic.com 2012-04-26 23:10:36 PDT ---
Commit pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/acc22ce25db42facfe4917aeceabd28a410f4c95
fix Issue 3866 - anonymous delegate with default parameters cross-talks to
another anonymous delegate

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |eco@gnuk.net


--- Comment #7 from Walter Bright <bugzilla@digitalmars.com> 2012-07-22 13:08:12 PDT ---
*** Issue 8258 has been marked as a duplicate of this issue. ***

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