• simendsjo <simendsjo gmail.com> Feb 24 2012
• Timon Gehr <timon.gehr gmx.ch> Feb 25 2012
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> Feb 27 2012
• simendsjo <simendsjo gmail.com> Feb 25 2012
• "Jonathan M Davis" <jmdavisProg gmx.com> Feb 27 2012

simendsjo <simendsjo gmail.com> writes:

I have a C function taking a callback function as a parameter. My thought  
was to wrap this up using a template, but I cannot get it to work:

extern(C) alias void function() Callback;

template Wrap(alias dg)
{
     extern(C) void Wrap()
     {
         dg();
     }
}

void main()
{
     Callback cb = &Wrap!( () {} );
}

Error: cannot implicitly convert expression (&Wrap) of type void  
delegate() pure nothrow  safe to extern (C) void function()

Timon Gehr <timon.gehr gmx.ch> writes:

On 02/24/2012 07:22 PM, simendsjo wrote:
 I have a C function taking a callback function as a parameter. My
 thought was to wrap this up using a template, but I cannot get it to work:

 extern(C) alias void function() Callback;

 template Wrap(alias dg)
 {
 extern(C) void Wrap()
 {
 dg();
 }
 }

 void main()
 {
 Callback cb = &Wrap!( () {} );
 }

 Error: cannot implicitly convert expression (&Wrap) of type void
 delegate() pure nothrow  safe to extern (C) void function()


This is a bug. '() {}' should be inferred as void function()pure nothrow 
 safe. Workaround: The code compiles if you use function() {} instead. I 
don't know if a bug report exists already.

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 02/25/2012 08:12 AM, Timon Gehr wrote:
 On 02/24/2012 07:22 PM, simendsjo wrote:
 I have a C function taking a callback function as a parameter. My
 thought was to wrap this up using a template, but I cannot get it to
 work:

 extern(C) alias void function() Callback;

 template Wrap(alias dg)
 {
 extern(C) void Wrap()
 {
 dg();
 }
 }

 void main()
 {
 Callback cb = &Wrap!( () {} );
 }

 Error: cannot implicitly convert expression (&Wrap) of type void
 delegate() pure nothrow  safe to extern (C) void function()


 This is a bug. '() {}' should be inferred as void function()pure nothrow
  safe.


Not according to the spec: "If the keywords function or delegate are 
omitted, it defaults to being a delegate"

   http://dlang.org/expression.html#FunctionLiteral

 Workaround: The code compiles if you use function() {} instead.


If I read the spec correctly, one must use the 'function' keyword.

Ali

simendsjo <simendsjo gmail.com> writes:

On Sat, 25 Feb 2012 17:12:50 +0100, Timon Gehr <timon.gehr gmx.ch> wrote:

 On 02/24/2012 07:22 PM, simendsjo wrote:
 I have a C function taking a callback function as a parameter. My
 thought was to wrap this up using a template, but I cannot get it to  
 work:

 extern(C) alias void function() Callback;

 template Wrap(alias dg)
 {
 extern(C) void Wrap()
 {
 dg();
 }
 }

 void main()
 {
 Callback cb = &Wrap!( () {} );
 }

 Error: cannot implicitly convert expression (&Wrap) of type void
 delegate() pure nothrow  safe to extern (C) void function()


 This is a bug. '() {}' should be inferred as void function()pure nothrow  
  safe. Workaround: The code compiles if you use function() {} instead. I  
 don't know if a bug report exists already.


Thanks. http://d.puremagic.com/issues/show_bug.cgi?id=7585

"Jonathan M Davis" <jmdavisProg gmx.com> writes:

On Monday, February 27, 2012 16:42:06 Ali Çehreli wrote:
 On 02/25/2012 08:12 AM, Timon Gehr wrote:
 On 02/24/2012 07:22 PM, simendsjo wrote:
 I have a C function taking a callback function as a parameter. My
 thought was to wrap this up using a template, but I cannot get it to
 work:
 
 extern(C) alias void function() Callback;
 
 template Wrap(alias dg)
 {
 extern(C) void Wrap()
 {
 dg();
 }
 }
 
 void main()
 {
 Callback cb = &Wrap!( () {} );
 }
 
 Error: cannot implicitly convert expression (&Wrap) of type void
 delegate() pure nothrow  safe to extern (C) void function()


 This is a bug. '() {}' should be inferred as void function()pure nothrow
  safe.


 Not according to the spec: "If the keywords function or delegate are
 omitted, it defaults to being a delegate"
 
 http://dlang.org/expression.html#FunctionLiteral
 
 Workaround: The code compiles if you use function() {} instead.


 If I read the spec correctly, one must use the 'function' keyword.


TDPL says that it's inferred, and I believe that work was recently done in 
improving the compiler's ability to infer it. So, in this case, the spec is 
almost certainly wrong.

- Jonathan M Davis