Without this, attempts to savestate std::set will fail with an error
about dropping the const qualifier.
<Lioncash> leoetlino: I'll try to break it down: So, when you do a
ranged-for on a container, it's essentially syntactic sugar over begin
and end iterators. std::set is an associative container where the key
type is the same as the value type, and so it's required that all
iterator functions return constant iterators. If this wasn't a
requirement, it would allow changing the ordering of elements from
outside of the set's API (this is bad).
Léo Lam
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