Is there any reason to use std::map::emplace() instead of try_emplace() in C++1z?

Question

In C++17, std::map and std::unordered_map got a new member-function template: try_emplace(). This new addition, proposed in n4279, behaves similarly to emplace(), but has th

Answer 1

try_emplace also doesn't support heterogenous lookup - it can't, because it takes the key.

Suppose we have a std::map> counts; and a std::string_view sv. I want to do the equivalent of ++counts[std::string(sv)];, but I don't want to create a temporary std::string, which is just wasteful, especially if the string is already present in the map. try_emplace can't help you there. Instead you'd do something like

if(auto lb = counts.lower_bound(sv); lb != counts.end() && lb->first == sv) {
    ++lb->second;
}
else {
    counts.emplace_hint(lb, sv, 1);
}