Why is map<bool,int> m={{1,2},{3,4},{5,0}}; size 1 and not 3?

Question

Quite peculiar:

map<bool,int> mb={{1,2},{3,4},{5,0}};
cout << mb.size(); 
map<int,int> mi={{1,2},{3,4},{5,0}};
cout << mi.size();

prints out

13

Answer 1

std::map is unique-key. 1, 3, 5 all yield true when converted to bool.