Use unordered_map with Custom Keys

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 $(0, 1)$ is not smaller or larger than $(1, 0)$, it simply points in a different direction. In such cases, we may still use the unordered_map type. Let's look at how to do this.

How to do it

For this recipe we'll create an unordered_map object that uses $x/y$ coordinates for the key. We will need a few support functions for this.

• First, we'll define a structure for the coordinates: