alt Hacker NewsWhy is this a perf footgun? As someone who doesn't write a lot of c++, I don't see anything intuitively wrong.
Is it that iterating over map yields something other than `std::pair`, but which can be converted to `std::pair` (with nontrivial cost) and that result is bound by reference?
Close, it is a std::pair, but it differs in constness. Iterating a std::map<K, V> yields std::pair<const K, V>, so you have:
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