Implicit conversion vs implicit constructor

[leonid-s-usov]

Channel

This is a "C++Weekly" episode request.

Topics

Suddenly I got puzzled what happens if class B with an implicit conversion to A is passed as an argument to parameter type A with an implicit constructor from const B&. I was surprised! https://godbolt.org/z/EabPGnY4z

• gcc compiles and calls the constructor of A(const B&) and ignores the conversion o_0
• msvc gives a strange error that an "operator could not be called" 🫤
• llvm detects and reports a conversion ambiguity with the two candidates listed💪💪

Length

This should be bite-sized (5-10 minutes) episode

[Dharmesh946]

Rules about what conversion chains are considered (or not) in C++ are indeed not always crystal clear. An educational presentation would be appreciated... (along with best-practices).