Out position
An out position is a type-parameter usage position in which values of the parameterized type are produced or returned rather than consumed.
Kotlin in Action, 2E
An out position is a type-parameter usage position in which values of the parameterized type are produced rather than consumed.
- How it is used
- Constrains generic APIs to producer-only use so subtype relationships remain safe.
- How deep it goes
- Explains return and parameter positions, declaration-site restrictions, covariance, and collection examples without descending into runtime implementation.
- Examples
- Uses Producer, Herd<Cat>, Herd<Animal>, List, and MutableList to contrast producing values with consuming them.
- What you can do after
- Apply it via Kotlin's out modifier to design producer-like generic types with safe covariance.
Fabulous Adventures in Data Structures and Algorithms
An output position is a type-parameter occurrence where values of the parameterized type are produced or returned rather than consumed.
- How it is used
- Uses output positions to determine when generic interfaces can safely support covariance.
- How deep it goes
- Explains returned values, getters, consumed parameters, and an extension-method workaround, then connects them to type safety.
- Examples
- Uses IEnumerable<T>, IE<T>, an immutable stack, and Animal, Giraffe, and Tiger assignments.
- What you can do after
- Apply it via C# generic interfaces to recognize safe covariance and relocate consuming operations into extension methods.
Read how Fabulous Adventures in Data Structures and Algorithms explains out position →
Related concepts
- covarianceused by · Covariance is a type-system property in which subtyping of a type argument induces the same-direction subtyping relationship for its parameterized type.
- in positioncontrasts with · An in position is a type-parameter usage position in which values of the parameterized type are accepted or consumed rather than produced.
- out keywordconfigured by · The out keyword declares a Kotlin generic type parameter as covariant and restricts its use to out positions.
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