TKey

TKey is a symbolic name commonly used in programming to denote the type of keys in generic data structures such as dictionaries, maps, or sets. It is not a single standardized type, but rather a conventional placeholder chosen by developers and language libraries to describe the role of the key in a collection that pairs keys with values.

In generic programming, a data structure that associates values with keys is parameterized by two types: the key type (often written as TKey) and the value type (often written as TValue). This naming helps convey intent in code and documentation. The key type typically needs to support efficient equality checks and hashing, because operations like lookups, insertions, and removals rely on comparing keys and distributing them in a hash-based container.

Common languages use TKey as part of their generic type declarations. For example, a dictionary or map might be declared as Dictionary<TKey, TValue> in languages with C-style generics, or as Map<TKey, TValue> in other ecosystems. While TKey is a conventional name, any compatible type can serve as a key, provided it implements the required semantics for equality and, if applicable, hashing.

Variations exist where TKey is a concrete class or type alias defined by a library, or where a language uses alternative parameter names such as K, Key, or TKey. When designing or using a keyed collection, attention to the key’s immutability, equality, and hash behavior is essential to ensure reliable and predictable lookups.