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

The third version uses the conditional operator to determine the common type. Its rules are described at quite a length in section 5.16 of the standard, so I'm not sure I should copy them here.

Simply put, the expression:

boolean-expression ? second-operand : third-operand

has a "common type" of the second and third operands, if such exists. The decltype specifier is then used to "convert" the expression into a type-specifier.