keypath

A key path is a sequence of keys or property names that specifies how to navigate a nested data structure to reach a particular value. Key paths can be represented as strings, arrays of keys, or language-specific path objects, and they are used to access or query data within objects, dictionaries, arrays, or JSON-like structures.

In different programming ecosystems, key paths have different semantics. In Cocoa and Cocoa Touch, key paths are used with key-value coding and key-value observing to access properties dynamically via strings, for example "address.city". In Swift, the KeyPath<Root, Value> type provides a type-safe way to refer to properties, as in let path = \Person.name. In JavaScript and many JSON-handling libraries, dot-separated paths such as "user.profile.email" identify nested fields. JSONPath and XPath offer more powerful query languages with similar ideas.

Common uses include retrieving nested values, binding user interfaces to data models, sorting or filtering collections by a nested property, and expressing queries against structured data. Key paths can also enable dynamic property access in data transformation pipelines.

Limitations include potential runtime errors when a path does not exist, especially for string-based paths, and reduced compile-time safety in dynamic languages. Complex keys may require escaping or alternative representations. Performance may be impacted by repeated path resolution.

See also: key-value coding, key-value observing, JSONPath, XPath, property path.