Conditional compilation on availability?

[Kirk McDonald]

Fredrik Olsson wrote:
> Might be an easy one, or a missing feature :).
> 
> But how do I do a conditional compilation on the availability of a 
> function, variable, type or whatever?
> 
> For example:
> 
> class foo(T) {
>  T[] bar;
>   static if ("predicate for toString(T) exists") {
>     char[] allBarsConcatinatedAsString() {
>       char[] r = ""
>       foreach (v; bar) {
>     r ~= toString(v);
>       }
>     }
>   }
> }
> 
> What would I type instead of "predicate for toString(T) exists"?
> 
> // Fredrik

class foo(T) {
     static if (is(typeof(toString(T.init)))) {
         // ...
     }
}

The IsExpression tests whether a given type is valid. typeof gets the 
type of a given expression. Thus, you can use one inside the other to 
test whether a given expression exists. Additionally, the expression 
inside of typeof is not actually executed, so it's safe to "call" the 
function like this.

-- 
Kirk McDonald
Pyd: Wrapping Python with D
http://dsource.org/projects/pyd/wiki