lancet/docs/function.md

Function

Package function can control the flow of function execution and support part of functional programming.

Source:

• https://github.com/duke-git/lancet/blob/main/function/function.go
• https://github.com/duke-git/lancet/blob/main/function/watcher.go

Usage:

import (
    "github.com/duke-git/lancet/v2/function"
)

Index

• After
• Before
• CurryFn
• Compose
• Debounced
• Delay
• Schedule
• Pipeline
• Watcher

Documentation

After

Creates a function that invokes given func once it's called n or more times.

Signature:

func After(n int, fn any) func(args ...any) []reflect.Value

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
)

func main() {
    fn := function.After(2, func() {
        fmt.Println("hello")
    })

    fn()
    fn()

    // Output:
    // hello
}

Before

creates a function that invokes func once it's called less than n times.

Signature:

func Before(n int, fn any) func(args ...any) []reflect.Value

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
    "github.com/duke-git/lancet/v2/internal"
)

func main() {
    fn := function.Before(2, func() {
        fmt.Println("hello")
    })

    fn()
    fn()
    fn()
    fn()

    // Output:
    // hello
    // hello
}

CurryFn

Make curry function.

Signature:

type CurryFn[T any] func(...T) T
func (cf CurryFn[T]) New(val T) func(...T) T

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
)

func main() {
    add := func(a, b int) int {
        return a + b
    }

    var addCurry function.CurryFn[int] = func(values ...int) int {
        return add(values[0], values[1])
    }
    add1 := addCurry.New(1)

    result := add1(2)

    fmt.Println(result)

    // Output:
    // 3
}

Compose

Compose the function list from right to left, then return the composed function.

Signature:

func Compose[T any](fnList ...func(...T) T) func(...T) T

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
)

func main() {
    toUpper := func(strs ...string) string {
        return strings.ToUpper(strs[0])
    }
    toLower := func(strs ...string) string {
        return strings.ToLower(strs[0])
    }
    transform := function.Compose(toUpper, toLower)

    result := transform("aBCde")

    fmt.Println(result)

    // Output:
    // ABCDE
}

Debounced

Creates a debounced function that delays invoking fn until after wait duration have elapsed since the last time the debounced function was invoked.

Signature:

func Debounced(fn func(), duration time.Duration) func()

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
)

func main() {
    count := 0

    add := func() {
        count++
    }

    debouncedAdd := function.Debounced(add, 50*time.Microsecond)

    debouncedAdd()
    debouncedAdd()
    debouncedAdd()
    debouncedAdd()

    time.Sleep(100 * time.Millisecond)

    fmt.Println(count)

    debouncedAdd()

    time.Sleep(100 * time.Millisecond)

    fmt.Println(count)

    // Output:
    // 1
    // 2
}

Delay

Invoke function after delayed time.

Signature:

func Delay(delay time.Duration, fn any, args ...any)

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
)

func main() {
    var print = func(s string) {
        fmt.Println(s)
    }

    function.Delay(2*time.Second, print, "hello")

    // Output:
    // hello
}

Schedule

Invoke function every duration time, until close the returned bool chan.

Signature:

func Schedule(d time.Duration, fn any, args ...any) chan bool

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
)

func main() {
    count := 0

    increase := func() {
        count++
    }

    stop := function.Schedule(2*time.Second, increase)

    time.Sleep(2 * time.Second)
    close(stop)

    fmt.Println(count)

    // Output:
    // 2
}

Pipeline

Pipeline takes a list of functions and returns a function whose param will be passed into the functions one by one.

Signature:

func Pipeline[T any](funcs ...func(T) T) func(T) T

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
)

func main() {
    addOne := func(x int) int {
        return x + 1
    }
    double := func(x int) int {
        return 2 * x
    }
    square := func(x int) int {
        return x * x
    }

    fn := function.Pipeline(addOne, double, square)

    result := fn(2)

    fmt.Println(result)

    // Output:
    // 36
}

Watcher

Watcher is used for record code excution time. can start/stop/reset the watch timer. get the elapsed time of function execution.

Signature:

type Watcher struct {
    startTime int64
    stopTime  int64
    excuting  bool
}
func NewWatcher() *Watcher
func (w *Watcher) Start() //start the watcher
func (w *Watcher) Stop() //stop the watcher
func (w *Watcher) Reset() //reset the watcher
func (w *Watcher) GetElapsedTime() time.Duration //get the elapsed time of function execution

Example:

package main

import (
    "fmt"
    "github.com/duke-git/lancet/v2/function"
)

func main() {
       w := function.NewWatcher()

    w.Start()

    longRunningTask()

    fmt.Println(w.excuting) //true

    w.Stop()

    eapsedTime := w.GetElapsedTime().Milliseconds()

    fmt.Println(eapsedTime)

    w.Reset()
}

func longRunningTask() {
    var slice []int64
    for i := 0; i < 10000000; i++ {
        slice = append(slice, int64(i))
    }
}