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digitalmars.D.bugs - [Issue 4288] New: Error on passing delegate to C linkage function.

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4288

           Summary: Error on passing delegate to C linkage function.
           Product: D
           Version: 1.057
          Platform: x86
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: adam.chrapkowski gmail.com


--- Comment #0 from Adam Chrapkowski <adam.chrapkowski gmail.com> 2010-06-06
09:24:38 PDT ---
Error occurs, when you try to use a delegate as a parameter to a C linked
function.

ex:
extern (C)
void c_func(void delegate() dg);
void d_func(void delegate() dg) { c_func(dg); }

Error: function test.c_func (void delegate()) does not match parameter types
(void delegate())
Error: cannot implicitly convert expression (dg) of type void delegate() to
void delegate()

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4288


Robert Clipsham <robert octarineparrot.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |robert octarineparrot.com


--- Comment #1 from Robert Clipsham <robert octarineparrot.com> 2010-06-06
17:59:33 BST ---
I don't think this bug is valid, something does need to be done about it
though. The following works:
----
alias extern(C) void delegate() cdg;
extern (C)
void c_func(void delegate() dg);
void d_func(cdg dg) { c_func(dg); }
----
So the problem is the linkage of the delegates doesn't match, there's no way to
get around it without an alias though, you can't have extern(C) in the function
parameters. Either the error needs improving, or there needs to be a way to
specify the linkage in the function args.

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--- Comment #2 from Adam Chrapkowski <adam.chrapkowski gmail.com> 2010-06-06
11:11:41 PDT ---
So two questions:

1. Why the following is allowed:
extern (C) void c_func(void delegate());
?

2. What does mean extern (C) void delegate() ?

Delegate is just a 'data structure which consists of two pointers' and anything
more. Something like C delegate does not exists. Linkage is related to
functions not data structures delegate is a data structure.

So if D data structures are disallowed in C functions why the following is
allowed?
extern (C) void c_func(string, Foo);
class Foo{...}
void d_func() {
  scope  foo = new Foo();
  string str = "Hello World!";
  c_func(str, foo);
}

string is a data structure as delegate, foo is a pointer to a data structure.

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klickverbot <code klickverbot.at> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |code klickverbot.at


--- Comment #3 from klickverbot <code klickverbot.at> 2012-05-12 07:40:25 PDT
---
Error message fix:

https://github.com/D-Programming-Language/dmd/pull/943

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prev sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

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


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