Problem with templates

[Clemens Hofreither]

Sean Reque Wrote:

> Could someone help me understand why this function doesn't work?
> 
> R delegate(T) my_compose(R, IR, IT, T...)(IR delegate(T) first, R delegate(IT) second) {
>   return delegate(T args) { second(first(args)); };
> }
> 
> I attempt to invoke the function like this:
> 
>   my_compose(&SQLAllocHandle, &SQL)(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &env);
> 
> where SQLAllocHandle is a C function that returns a short and SQL is a function that accepts a short as its only parameter. I get the following error:
> 
> test.d(35): template test.my_compose(R,IR,IT,T...) does not match any function template declaration
> test.d(35): template test.my_compose(R,IR,IT,T...) cannot deduce template function from argument types !()(shortC  function(short, void*, void**),void function(short rc))
> test.d(35): Error: function expected before (), not (my_compose(R,IR,IT,T...))((& SQLAllocHandle),(& SQL)) of type int
> 
> 
> I am using two separate template types, IR and IT, because according to the error message function 1 returns a shortC and function two accepts a short. I assume a shortC is implicitly convertible to a short :). I am guessing the shortC comes from the fact that SQLAllocHandle is an extern(C) function. 
> 
> I tried to model this function off of the Curry example in d 2.0 on this page: http://digitalmars.com/d/2.0/template.html. I am using version 2.015. I really don't understand how what I am doing is any different conceptually than this curry example, which works fine.
> 
> 

Have you tried using "function" instead of "delegate"? AFAIK, delegates refer to object member functions, whereas functions are global functions. Since your functions come from C, they'd certainly be global functions.

-Clemens