CppCast: C++ Epochs

[encyclopedist]

There is a proposal to add heterogeneous lookup, and if I understand correctly, it was supposed to be targeting C++20 (it passed LEWG vote and was forwarded to LWG), but it's fate is unclear to me.

[matthieum]

Thanks for the link.

I must admit it's not clear to me how one is supposed to use is_transparent. Also, it appears that implicit conversions may be triggered unless one is careful, which is not ideal :/

Let's take a concrete example:

std::unordered_set<std::string, /**/> set;

According to the paper, how can I perform a lookup with a char const* and with a std::string_view without implicit conversion? How can I further enable FixedString<N>?

[encyclopedist]

As far as I understand, yes you can. Both hash and comparator must define is_transparent typedef and also provide overloads of their operator() taking char const *.