Introduction

Map

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func MapStrToStr(arr []string, fn func(s string) string) []string {
    var sl []string
    for _, s := range arr {
        sl = append(sl, fn(s))
    }
    return sl
}

func MapStrToInt(arr []string, fn func(s string) int) []int {
    var sl []int
    for _, s := range arr {
        sl = append(sl, fn(s))
    }
    return sl
}

func main() {
    list := []string{"hello", "world"}

    x := MapStrToStr(list, func(s string) string {
        return strings.ToUpper(s)
    })
    fmt.Printf("%v\n", x) // [HELLO WORLD]

    y := MapStrToInt(list, func(s string) int {
        return len(s)
    })
    fmt.Printf("%v\n", y) // [5 5]
}

Reduce

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func Reduce(arr []string, fn func(s string) int) int {
    sum := 0
    for _, s := range arr {
        sum += fn(s)
    }
    return sum
}

func main() {
    list := []string{"hello", "world"}
    x := Reduce(list, func(s string) int {
        return len(s)
    })
    println(x) // 10
}

Filter

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func Filter(arr []int, fn func(n int) bool) []int {
    var sl []int
    for _, n := range arr {
        if fn(n) {
            sl = append(sl, n)
        }
    }
    return sl
}

func main() {
    sl := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}

    even := Filter(sl, func(n int) bool {
        return n%2 == 0
    })
    fmt.Printf("%v\n", even) // [0 2 4 6 8]

    odd := Filter(sl, func(n int) bool {
        return n%2 != 0
    })
    fmt.Printf("%v\n", odd) // [1 3 5 7 9]
}

Generic

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func GenericMap[T, U any](arr []T, fn func(T) U) []U {
    var sl []U
    for _, s := range arr {
        sl = append(sl, fn(s))
    }
    return sl
}

func main() {
    list := []string{"hello", "world"}

    x := GenericMap(list, func(s string) string {
        return strings.ToUpper(s)
    })
    fmt.Printf("%v\n", x) // [HELLO WORLD]

    y := GenericMap(list, func(s string) int {
        return len(s)
    })
    fmt.Printf("%v\n", y) // [5 5]
}