Associated type
An associated type is a type member declared by a trait or similar abstraction whose concrete type is specified by each implementation.
Learn Rust in a Month of Lunches
An associated type is a type declaration attached to a Rust trait whose concrete value is specified for each implementation.
- How it is used
- Uses associated types to connect trait behavior with implementation-specific result types in iterators, futures, and arithmetic.
- How deep it goes
- Defines the syntax and works through custom and standard traits, but defers deeper details of pinning and asynchronous internals.
- Examples
- Demonstrates Iterator::Item, Future::Output, Add::Output, and a ChangeForm trait implemented for String and i32.
- What you can do after
- Apply associated types by declaring them in traits and choosing concrete types when implementing those traits.
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Functional Design and Architecture: Examples in Haskell
An associated type is a type member declared within a type class or similar abstraction and determined by its implementing type.
- How it is used
- Uses associated types to connect entities with database-specific keys and values in a generic, type-safe persistence interface.
- How deep it goes
- Explains declarations, concrete instances, and generic use, while stopping short of a broader formal treatment of type-level programming.
- Examples
- Demonstrates MeteorEntity and CometEntity instances with distinct keys, stored values, conversions, and a generic loadEntity function.
- What you can do after
- Build it from scratch by declaring entity-specific associated types and implementing generic key, value, and conversion operations.
Read how Functional Design and Architecture: Examples in Haskell explains associated type →
Related concepts
- Derefused by · Deref is a Rust standard-library trait that defines how a value is dereferenced to access a target value and enables dereference coercions.
- algebraic data typekind of · An algebraic data type is a composite type whose values are formed from product structures, finite alternatives, or both through type constructors.
- traitpart of · A trait is a type-level construct that defines reusable behavior or members that types can implement or compose.
- type classused by · A type class is a language feature defining operations and constraints that types can satisfy to support ad hoc polymorphism.
- futurepart of · A future is an abstraction representing an asynchronous computation or its result, which may not be complete or available yet.
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