C++17: insert_or_assign - new API for associative containers

1. Before C++17
This new API ticks a few boxes for our daily programming. Think of the scenario that insert into the container if the key does not exist and update the value if it does exist. Before C++17 it has to use the combination of the following 3 calls as shown in Figure 1.
    - find
    - insert/emplace
    - operator []

Figure 1. Implementation before C++17

Note: emplace() is recommended other than insert() for better performance.

The reason why not use operator [] directly, please refer to Item 24 in [1]. There Scott Meyer has detailed discussion about the performance between operator [] and insert.

2. C++17
From C++17 on the solutions shown in Figure 1 can be replace with this new API - insert_or_assign() as shown in Figure 2.

Figure 2. Implementation in C++17 with the New API

I have looked at the assembly for the code under VS2015 and this is no performance penalty. Therefore feel free and happy to use.


Bibliography:
[1] Scott Meyers, Effectie STL 50 Specific Ways to Improve Your Use of the Standard Template Library