KeyValuePair

KeyValuePair is a basic data structure that stores two related items: a key and its associated value. It is used to model associations in dictionaries, maps, and other data collections where data is looked up by a key. In many languages the key identifies the value within a container, while the value holds the stored data.

In C#, KeyValuePair<TKey, TValue> is a value type defined in System.Collections.Generic. It represents a single association and is commonly produced when iterating over a dictionary. The type is immutable: it exposes public Key and Value properties and a constructor KeyValuePair(TKey key, TValue value).

Java uses Map.Entry<K, V> as the corresponding concept. Entries are provided by map implementations and typically expose getKey(), getValue(), and setValue() in mutable implementations; however the interface itself does not require mutability.

Key-value stores and databases use the broader term to describe storage models where data is addressed by a key. Examples include in-memory caches and distributed stores, where the key identifies the stored value and operations include put/get/delete. Values can be binary data, strings, or structured data.

Usage and properties: Keys are unique within a collection, so a KeyValuePair represents a single mapping. They are convenient for enumerating all associations, serializing pairs for transmission, or exposing a uniform API for dictionary-like structures. Performance depends on the underlying container: hash-based maps typically offer average O(1) lookups, while tree-based maps offer O(log n) performance.