Swift – Return a Function from another Function

To return a Function b from another Function a in Swift, specify the complete parameters and return type of function b as return type of the function a.

The return type of function a is formed from the parameters and return type of function b.

The syntax to return a function b from function a is

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func a(parameters) -> (Function_b_Parameters_Type) -> Function_b_ReturnType {
    func b (someParameters) -> ReturnType {
        //body
    }
}

Examples

In the following program, we will return addition() function from calculate() function.

main.swift

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func calculate() -> (Int, Int) -> Int {

    func addition(a: Int, b: Int) -> Int {
        return a + b
    }
  
    return addition
}

//variable to store function
var myFunc: (Int, Int) -> Int

myFunc = calculate()
print("Addition")
print(myFunc(2, 5))

In the following program, we will return any of the function addition(), subtraction(), multiplication() or division(), from function calculate() based on parameter passed to calculate() function.

main.swift

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func calculate(operation: String) -> (Int, Int) -> Int {
    func addition(a: Int, b: Int) -> Int {
        return a + b
    }

    func subtraction(a: Int, b: Int) -> Int {
        return a - b
    }

    func multiply(a: Int, b: Int) -> Int {
        return a * b
    }

    func division(a: Int, b: Int) -> Int {
        return a / b
    }
    
    switch operation {
    case "+":
        return addition
    case "-":
        return subtraction
    case "*":
        return multiply
    case "/":
        return division
    default:
        return addition
    }
}

//variable to store function
var myFunc: (Int, Int) -> Int

myFunc = calculate(operation: "+")
print("Addition")
print(myFunc(2, 5))

myFunc = calculate(operation: "-")
print("Subtraction")
print(myFunc(2, 5))

myFunc = calculate(operation: "*")
print("Multiplition")
print(myFunc(2, 5))

myFunc = calculate(operation: "/")
print("Division")
print(myFunc(2, 5))

Output

Swift - Return a Function from another Function - Example

Conclusion

In this Swift Tutorial, we learned how to return a function from another function in Swift.