How to Define Function Types in Go

Define function types in Go using the func keyword followed by parameter and return types in parentheses. Use this syntax to declare variables that hold functions or to define custom type aliases for function signatures.

// Declare a variable with a function type
var add func(int, int) int

// Define a custom type alias for a function signature
type MathOp func(float64, float64) float64

// Assign a function to the variable
add = func(a, b int) int {
    return a + b
}

A function type describes the shape of a function by listing its inputs and outputs without naming the function itself. You use this to create variables that can store different functions as long as they match that specific shape. Think of it like a mold for a specific type of tool; any tool fitting that mold can be used in that slot.