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# 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: ​

go

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

    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:

go

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

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

Example:Run

go

    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
    }

    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:

go

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

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

Example:Run

go

    package main

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

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

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

        // Output:
        // hello
        // hello
    }

    package main

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

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

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

        // Output:
        // hello
        // hello
    }

### CurryFn ​

Make curry function.

Signature:

go

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

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

Example:Run

go

    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
    }

    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:

go

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

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

Example:Run

go

    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
    }

    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:

go

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

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

Example:Run

go

    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
    }

    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:

go

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

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

Example:Run

go

    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
    }

    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:

go

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

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

Example:Run

go

    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
    }

    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:

go

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

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

Example:Run

go

    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
    }

    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:

go

    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

    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:Run

go

    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))
        }
    }

    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))
        }
    }