std::common_type implementation

Question

Just to see how it worked, I looked at the libstdc++ implementation of std::common_type in the header type_traits. I have to admit that I don\'t really

Answer 1

Long Story Short: The decltype is making the C++ compiler determine the closest ancestor type for it.

Tertiary Operator's have the resulting static type of the closest ancestor of the two possible expressions.

E.g:

A inherits from B

X inherits from Y inherits from B

 ?  :  
    =   // this is how the C++ parser sees it

This is how the C++ language works. The decltype just makes the typedef be the static type of the result of that expression (whatever type the C++ compiler determines it to be)