test if object is instance of class at compile time

[Jacob Carlborg]

On 2011-12-21 21:15, Elvis Maehren wrote:
> This works fine at runtime, but explodes in CTFE:
> ---
> bool isInstanceOf(T, O)(O o) {
> 	return (cast(T) o) !is null;
> }
> ---
>
> CTFE doesn't like "!is null" ("cannot compare [...] at compile time").
>
> Moreover, in CTFE a failed cast terminates the interpretation ("cannot
> reinterpret class from [...] to [...] at compile time"). Is this somehow
> catchable? If so, I could do something along these lines:
> ---
> if(__ctfe) {
> 	try {
> 		auto t = cast(T) o;
> 		return true;
> 	} catch {
> 		return false;
> 	}
> }
> ---
>

I don't think you can do a test like that during compile time. In your 
above function, isInstanceOf, "o" will always be of the type "O". You 
can always do a comparisons to see if O is the same type as T.

-- 
/Jacob Carlborg