stdhashT

stdhashT is a template-based hashing utility designed for use with hash-based containers and generic algorithms. It provides a function object that maps values of type T to a size_t hash value and is intended to support policy-based customization in addition to conventional hashing behavior.

Template parameters and interface: The primary template parameters are T, the value type to be hashed, and Policy, a hashing policy that defines how the hash value is computed. The typical public interface consists of an operator() that takes a const T& and returns a size_t. In common implementations, the hash object is stateless, allowing it to be copied and stored efficiently as a hasher in containers such as unordered_map or unordered_set.

Customization and policies: A key design goal of stdhashT is to enable customized hashing strategies through policies. A user can provide a specialized stdhashT<T, Policy> or a policy type that exposes a hash_value(const T&) method, a combine function, or both. This enables precise control over how composite types are hashed, such as combining multiple fields in a deterministic and distribution-friendly manner. Default policies may delegate to existing std::hash specializations for primitive or standard types, while more complex types can implement tailored hashing logic.

Usage: The hasher type stdhashT<T, Policy> can be supplied to standard hash-based containers as the third template argument. This allows consistent hashing of user-defined types across modules, provided a suitable policy is supplied. Like other standard hash mechanisms, the exact numerical values produced are implementation-defined and may vary across platforms and executions.

See also: std::hash, unordered_map, unordered_set, policy-based design, hash combine.