In position
An in position is a type-parameter usage position in which values of the parameterized type are accepted or consumed rather than produced.
Kotlin in Action, 2E
An in position is a type-parameter usage position in which values of the parameterized type are consumed rather than produced.
- How it is used
- Explains how generic type parameters are consumed by function parameters and how variance declarations constrain their use.
- How deep it goes
- Defines parameter and return positions, then connects them to covariance, contravariance, and nested type-argument checks.
- Examples
- Uses a consuming function parameter, covariant Herd, and read-only List to contrast in and out positions.
- What you can do after
- Apply it via Kotlin variance declarations by identifying whether each type-parameter use consumes or produces values.
Fabulous Adventures in Data Structures and Algorithms
An input position is a type-parameter occurrence where values of the parameterized type are accepted or consumed rather than produced.
- How it is used
- Defines why contravariant interfaces permit assignments that reverse the direction of ordinary type relationships.
- How deep it goes
- Explains consumed type parameters, demonstrates assignment compatibility, and connects reversed mappings to category-theoretic arrows.
- Examples
- Uses animal comparers, Giraffe and Animal types, and the `IC<in T>` interface.
- What you can do after
- Apply contravariance by declaring an input-only interface parameter with the C# `in` modifier.
Read how Fabulous Adventures in Data Structures and Algorithms explains in position →
Related concepts
- out positioncontrasts with · An out position is a type-parameter usage position in which values of the parameterized type are produced or returned rather than consumed.
- contravarianceused by · Contravariance is a type-system relationship in which subtyping between parameterized types reverses the subtyping relationship between their type arguments, typically for input positions.
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