Date: 2024dec19 Language: C++ Product: MSVC Q. MSVC: When std::unordered_map<> can be used A. When I used it inside a class I got "attempting to reference a deleted function". The top-voted answer by Barry on Stack Overflow explains the fine points https://stackoverflow.com/questions/31264984/c-compiler-error-c2280-attempting-to-reference-a-deleted-function-in-visual A quick rule of thumb for me that works is: - You can always use std::unordered_map at the file scope (Good for a cache, etc) - If you don't want to change you class's move and copy constructors use std::map instead. Its slower but compiles.