alt Hacker NewsWhile tag dispatching used to be a widely used idiom in C++ development, it was a workaround for which nowadays there are much better alternatives with constexpr, and concepts.
While tag dispatching used to be a widely used idiom in C++ development, it was a workaround for which nowadays there are much better alternatives with constexpr, and concepts.
Surely one of the obvious reasons you'd want tagged dispatch in C++ isn't obviated by either of those features? Or am I missing something?
Suppose Doodads can be constructed from a Foozle either with the Foozle Resigned or with the Foozle Submitted. Using tagged dispatch we make Resigned and Submitted types and the Doodad has two specialised constructors for the two types even though substantively we pass only the Foozle in both cases.
In a language like Rust all the constructors have names, it's obvious what Vec::with_capacity does while you will still see C++ programmers who thought constructing a std::vector with a single integer parameter does the same because it's just a constructor and you'd need to memorize what happens.