const_reference operator[](const typename object_t::key_type& key) const throw instead of assert

[smonasco]

Feature Request

I'd rather have an out_of_range exception thrown than undefined behavior that kills my app (VS2015).

[OvermindDL1]

Except by following the standard, operator[] is unchecked where a at should be checked. I.E. accessing an invalid key/index via operator[] is supposed to be UB. If you want a checked version then you should use an at (if this library doesn't have an at then it should be added, I don't recall...).

[nlohmann]

Duplicate: #264 #135

[nlohmann]

The behavior of const operator[] is documented. The goal is to have quick access without checking overhead. For the latter, there is at.

There have been long discussions about the behavior. In conclusion, we would rather have a const operator[] version with the current semantics than just a copy of at. We are aware of std::map not having a const operator[].

To be sure, always use at, or find in combination with operator[].

[smonasco]

OK, but there are no savings in doing the assert over the if and throw. The assert still must make the comaprison.

https://ideone.com/e.js/RyHb0t

Everytime I check the assert over 1,000,000 iterations it ends up being slower actually.

[nlohmann]

In production code, you should compile without assertions.