Function type
A function type is a type that specifies the parameter types and return type of callable values.
Kotlin in Action, 2E
A function type describes the parameter types and return type of callable values.
- How it is used
- Enables higher-order functions that receive, store, and return behavior as lambda or function-reference values.
- How deep it goes
- Explains syntax, invocation, nullability placement, named parameters, returned functions, and predicate-based reuse; defers lambda performance to inline functions.
- Examples
- Uses arithmetic operations, a String filter, shipping-cost selection, contact filtering, and site-visit duration queries.
- What you can do after
- Build it from scratch by declaring function-typed variables, parameters, and returns, then passing or invoking lambdas.
Learn Haskell by Example
A function type specifies the input and output types of a function value.
- How it is used
- Uses function types to document definitions, check operator compatibility, and shape practical encryption and synthesizer components.
- How deep it goes
- Explains unary and curried function types, lambda notation, syntactic sugar, and operator-driven type errors without covering deeper type-system internals.
- Examples
- Uses square and add definitions, mixed Int and Double multiplication, character rotation, and Event-to-Signal oscillators.
- What you can do after
- Evaluate and write Haskell signatures for unary, multi-argument, and function-valued definitions while diagnosing simple type mismatches.
Geometry for Programmers
A function type specifies the kinds of inputs and outputs a function accepts, including its domain and codomain.
- How it is used
- Frames geometric modeling functions by matching mathematical domains and codomains with programming input and output types.
- How deep it goes
- Defines domains and codomains, then distinguishes transformations and vector fields, without developing their later chapters’ mechanics.
- Examples
- Uses translation of a square in ℝ² and vector-field illustrations to ground abstract function types.
- What you can do after
- Evaluate/understand geometric functions by identifying their input spaces, output spaces, and per-input values.
100 Go Mistakes and How to Avoid Them
A function type is a Go type whose values are functions with a specified parameter and result signature.
- How it is used
- Uses function types to inject time dependencies and make unit tests deterministic.
- How deep it goes
- Defines a named function type, wires production and test implementations, and contrasts function injection with global state and explicit arguments.
- Examples
- Uses Cache, time.Now, TrimOlderThan, fixed timestamps, and a fake func() time.Time implementation.
- What you can do after
- Build deterministic time-dependent tests by injecting a function that returns a controlled timestamp.
Read how 100 Go Mistakes and How to Avoid Them explains function type →
Related concepts
- Kotlinused by · Kotlin is a statically typed general-purpose programming language that targets the JVM and other platforms and interoperates with Java.
- data typekind of · A data type is a classification that specifies the values data can represent, how they are represented or interpreted, and which operations apply to them.
- atomic typekind of · An atomic type is a type whose supported accesses and operations are indivisible with respect to concurrent execution and provide defined synchronization semantics.
- factorialequivalent to · The factorial of a nonnegative integer n, written n!, is the product of all positive integers from 1 through n, with 0! equal to 1.
- FunctionN interfaceequivalent to · A FunctionN interface is a compiler-generated Kotlin interface representing a function value with a specific number of parameters and an invoke operation.
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