Functions & Multiple Returns

package main

import (
    "errors"
    "fmt"
    "math"
)

// Basic function
func add(a, b int) int {
    return a + b
}

// Multiple return values — the Go idiom for error handling
func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, errors.New("division by zero")
    }
    return a / b, nil
}

// Named return values
func minMax(nums []int) (min, max int) {
    min, max = nums[0], nums[0]
    for _, n := range nums[1:] {
        if n < min { min = n }
        if n > max { max = n }
    }
    return  // "naked" return — returns named values
}

// Variadic function
func sum(nums ...int) int {
    total := 0
    for _, n := range nums {
        total += n
    }
    return total
}

// Function as a value
func apply(f func(float64) float64, x float64) float64 {
    return f(x)
}

func main() {
    fmt.Println(add(3, 4))   // 7

    result, err := divide(10, 3)
    if err != nil {
        fmt.Println("Error:", err)
    } else {
        fmt.Printf("%.4f\n", result)  // 3.3333
    }

    lo, hi := minMax([]int{3, 1, 4, 1, 5, 9, 2, 6})
    fmt.Println(lo, hi)   // 1 9

    fmt.Println(sum(1, 2, 3, 4, 5))   // 15

    // Passing a function
    fmt.Printf("%.4f\n", apply(math.Sqrt, 16))  // 4.0000

    // Anonymous function / closure
    multiplier := func(factor float64) func(float64) float64 {
        return func(x float64) float64 {
            return x * factor
        }
    }
    double := multiplier(2)
    triple := multiplier(3)
    fmt.Println(double(5), triple(5))  // 10 15
}