Insert on lookup is convenient but encourages either double-lookup patterns (contains + get) or unintentional inserts. I very much like Python's setdefault -- except for its 10-chars name.
if(auto i = x.find(y); i!=x.end()){
// use i->{first,second}
}
for(auto [key, value]: x.equal_range(y)) {
}
The equal_range solution looks nice from a genericity perspective (look ma I do multimaps!) but is really unintuitive with regular maps imo. Unless I'm mistaken it also does not allow an else branch for when the value is not there, which is often needed.
Hopefully one day we will get proper patter matching and destructing in if statements (Herb Sutter has made significant progress on this).
cpp2 is both interesting and ambitious, I really hope it gets somewhere.
OTOH, try...else I find myself missing at times.