Call a function with a function pointer

[Dicebot]

On Thursday, 10 October 2013 at 17:47:54 UTC, Namespace wrote:
> ----
> import std.stdio;
>
> void foo1(void function(void*) fp) { }
> void foo2(void function(int) fp) { }
> void foo3(void*) { }
>
> void main()
> {
> 	foo1((void* ptr) => ( assert(ptr is null) ));
> 	foo2((int a) => ( a + 1 )); /// Fails: Error: function foo2 
> (void function(int) fp) is not callable using argument types 
> (int function(int a) pure nothrow @safe)
> 	
> 	foo1(&foo3);
> 	
> 	void foo4(void function(void*) fp) { }
> 	foo1(&foo4); /// Fails: Error: function foo1 (void 
> function(void*) fp) is not callable using argument types (void 
> delegate(void function(void*) fp))
> }
> ----
> Can someone explain that to me?

You are using short lambda syntax "a => b". Here `b` is always 
return statement. It is equivalent to "(a) { return b; }". And 
your `foo2` signature expects lambda returning void, like "(a) { 
return; }"

Second error is DMD incompetence in deducing minimal required 
type of nested function. It always treats them as delegates (== 
having hidden context pointer) even if those do not refer any 
actual context. And plain lambdas are of course binary 
incompatible with delegates (closures) because of that extra 
pointer field.