Checking for possibility of implicit conversions

[H. S. Teoh]

How do I check if a given type T can be implicitly converted to some
type S at compile-time? I'm trying to write a signature constraint for a
template function that should only be instantiated if the parameter type
can be implicitly assigned to some given type S.

	struct S(T) {
		T value;

		void setValue(S)(S newValue)
			if ( /* ???? */ )
		{
			value = newValue;
		}

I tried __traits(compiles, value = newValue) but it seems to always
return true, and then later the compiler errors out at the actual
assignment statement. I'd like to be able to catch this at the signature
constraint instead of inside the function body.


T

-- 
If you look at a thing nine hundred and ninety-nine times, you are
perfectly safe; if you look at it the thousandth time, you are in
frightful danger of seeing it for the first time. -- G. K. Chesterton