std::map<>::insert using non-copyable objects and uniform initialization
Have a look at the following code:
#include
#include -
[This is a complete rewrite. My earlier answer had nothing to do with the problem.]
The
maphas two relevantinsertoverloads:insert(const value_type& value), andinsert(P&& value).
When you use the simple list-initializer
map.insert({1, non_copyable()});, all possible overloads are considered. But only the first one (the one takingconst value_type&) is found, since the other doesn't make sense (there's no way to magically guess that you meant to create a pair). The first overload doesn't work of course since your element isn't copyable.You can make the second overload work by creating the pair explicitly, either with
make_pair, as you already described, or by naming the value type explicitly:typedef std::mapNow the list-initializer knows to look for
map_type::value_typeconstructors, finds the relevant movable one, and the result is an rvalue pair which binds to theP&&-overload of theinsertfunction.(Another option is to use
emplace()withpiecewise_constructandforward_as_tuple, though that would get a lot more verbose.)I suppose the moral here is that list-initializers look for viable overloads – but they have to know what to look for!
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