Equivalent ternary operator for constexpr if?

Question

Maybe I missed something, but I can\'t find any hints: is there a constexpr ternary operator in C++17 equivalent to constexpr-if?

template

        

Answer 1

No, there is no constexepr conditional operator. But you could wrap the whole thing in a lambda and immediately evaluate it (an IIFE):

template
class BusAddress {
public:
    explicit constexpr BusAddress(Address device)
     : mAddress([&]{
          if constexpr (Mode::write) {
            return device.mDevice << 1;
          }
          else {
            return (device.mDevice << 1) | 0x01;
          }         
        }())
     { }
private:
    uint8_t mAddress = 0;    
};

It may not be the sexiest code ever, but it gets the job done. Note that lambdas are constexpr by default where possible as of N4487 and P0170.