Awesome! Thank you so much!
This literally saved me a lot of work. I was working on my own map implementation a while back, until Andreas pointed me here.
You nicely unified the code behind all containers, which really is a big plus.
The iterator additions make this complete. I love it.
I do prefer the standard bindings, so I'll change them like you suggested.
The extra safety measure will really come in handy as well. I can compile my engine with the security in debug, and without in release if it becomes relevant to increase performance after testing the game logic in debug. Perfect.