num::unordered_map

Defined in header <core/types.hpp>

template <class K, class V, class Hash = std::hash<K>, class Eq = std::equal_to<K>,
          class Alloc = std::allocator<std::pair<const K, V>>>
using unordered_map = std::unordered_map<K, V, Hash, Eq, Alloc>;

std::unordered_map: a hash map with no key order, like Rust HashMap.