computedproperty

A computed property is a property of an object whose value is derived from other data, rather than stored directly. Accessing it runs a calculation to produce a result, so the property represents a view of the current state rather than a fixed field.

Most languages implement computed properties through getters or accessors. The property is typically exposed as a read-only or read/write attribute, but the value is produced on demand.

In Python, the @property decorator defines a read-only computed attribute, with alternative cached_property for one-time results. In Swift, computed properties are defined with a get block and may include a set, without a backing store unless one is provided. In JavaScript, frameworks such as Vue.js expose computed properties as getters that depend on reactive data and are cached until their dependencies change.

Benefits include avoiding duplicated state, providing a clean API for derived information, and keeping related logic together. Potential downsides are performance costs for expensive computations and the risk of stale results if dependencies are not managed.

Common use cases include formatting names, computing aggregates, or deriving status flags from multiple inputs. Computed properties help maintain consistency by calculating values on demand rather than storing multiple derived fields, but they require careful consideration of when and how often the computation runs.