SFINAE + sizeof = detect if expression compiles

Question

I just found out how to check if operator<< is provided for a type.

template T& lvalue_of_type();
template

        

Answer 1

It is just a combination of two well-known tricks. SFINAE says 'substitution failure is not an error' - that's exactly what you did. Using sizeof to let the compiler substitute template arguments into an expression without actually executing it is also common.

Sorry :-)