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C++20 STL Cookbook

Use unordered_map with Custom Keys

Explore how to use std::unordered_map with custom key types in C++20. Learn to define a struct for keys, implement equality operators, and specialize std::hash to enable efficient access and storage of custom keys in unordered_map containers.

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With an ordered map, the type of the key must be sortable, which means it must at least support the less-than < comparison operator. Suppose we want to use an associative container with a custom type that is not sortable. For example, a vector where (0,1)(0, 1) is not smaller or larger than (1,0)(1, 0), it simply points in a different direction. In such cases, we may still use the ...