Using delegates in callbacks for extern(C) functions

[Jonathan M Davis]

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