lancet/docs/function.md

# Function

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

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## Source:

[https://github.com/duke-git/lancet/blob/v1/function/function.go](https://github.com/duke-git/lancet/blob/v1/function/function.go)
[https://github.com/duke-git/lancet/blob/v1/function/watcher.go](https://github.com/duke-git/lancet/blob/v1/function/watcher.go)

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## Usage:

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

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## Index

-   [After](#After)
-   [Before](#Before)
-   [Curry](#Curry)
-   [Compose](#Compose)
-   [Debounce](#Debounce)
-   [Debounced<sup>deprecated</sup>](#Debounced)
-   [Throttle](#Throttle)
-   [Delay](#Delay)
-   [Pipeline](#Pipeline)
-   [Schedule](#Schedule)
-   [Watcher](#Watcher)

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## Documentation

### <span id="After">After</span>

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

<b>Signature:</b>

```go
func After(n int, fn interface{}) func(args ...interface{}) []reflect.Value
```

<b>Example:</b>

```go
package main

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

func main() {
    arr := []string{"a", "b"}
    f := function.After(len(arr), func(i int) int {
        fmt.Println("last print")
        return i
    })

    type cb func(args ...interface{}) []reflect.Value
    print := func(i int, s string, fn cb) {
        fmt.Printf("arr[%d] is %s \n", i, s)
        fn(i)
    }

    fmt.Println("arr is", arr)
    for i := 0; i < len(arr); i++ {
        print(i, arr[i], f)
    }

    //output:
    // arr is [a b]
    // arr[0] is a
    // arr[1] is b
    // last print
}
```

### <span id="Before">Before</span>

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

<b>Signature:</b>

```go
func Before(n int, fn interface{}) func(args ...interface{}) []reflect.Value
```

<b>Example:</b>

```go
package main

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

func main() {
    assert := internal.NewAssert(t, "TestBefore")

    arr := []string{"a", "b", "c", "d", "e"}
    f := function.Before(3, func(i int) int {
        return i
    })

    var res []int64
    type cb func(args ...interface{}) []reflect.Value
    appendStr := func(i int, s string, fn cb) {
        v := fn(i)
        res = append(res, v[0].Int())
    }

    for i := 0; i < len(arr); i++ {
        appendStr(i, arr[i], f)
    }

    expected := []int64{0, 1, 2, 2, 2}
    assert.Equal(expected, res)
}
```

### <span id="Curry">Curry</span>

<p>Make a curry function.</p>

<b>Signature:</b>

```go
type Fn func(...interface{}) interface{}
func (f Fn) Curry(i interface{}) func(...interface{}) interface{}
```

<b>Example:</b>

```go
package main

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

func main() {
    add := func(a, b int) int {
        return a + b
    }
    var addCurry function.Fn = func(values ...interface{}) interface{} {
        return add(values[0].(int), values[1].(int))
    }
    add1 := addCurry.Curry(1)
    result := add1(2)
    fmt.Println(result) //3
}
```

### <span id="Compose">Compose</span>

<p>Compose the function list from right to left, then return the composed function.</p>

<b>Signature:</b>

```go
func Compose(fnList ...func(...interface{}) interface{}) func(...interface{}) interface{}
```

<b>Example:</b>

```go
package main

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

func main() {
    add1 := func(v ...interface{}) interface{} {
        return v[0].(int) + 1
    }
    add2 := func(v ...interface{}) interface{} {
        return v[0].(int) + 2
    }

    add3 := function.Compose(add1, add2)
    result := add3(1)

    fmt.Println(result) //4
}
```

### <span id="Debounced">Debounced</span>

<p>Creates a debounced function that delays invoking fn until after wait duration have elapsed since the last time the debounced function was invoked. This function is deprecated. use Debounce instead.</p>

<b>Signature:</b>

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

<b>Example:</b>

```go
package main

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

func main() {
    count := 0
    add := func() {
        count++
    }

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

    time.Sleep(100 * time.Millisecond)
    fmt.Println(count) //1

    function.debouncedAdd()
    time.Sleep(100 * time.Millisecond)
    fmt.Println(count) //2
}
```

### <span id="Debounce">Debounce</span>

<p>Creates a debounced version of the provided function. The debounced function will only invoke the original function after the specified delay has passed since the last time it was invoked. It also supports canceling the debounce.</p>

<b>Signature:</b>

```go
func Debounce(fn func(), delay time.Duration) (debouncedFn func(), cancelFn func())
```

<b>Example:</b>

```go
package main

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

func main() {
    callCount := 0
    fn := func() {
        callCount++
    }

    debouncedFn, _ := function.Debounce(fn, 500*time.Millisecond)

    for i := 0; i < 10; i++ {
        debouncedFn()
        time.Sleep(50 * time.Millisecond)
    }

    time.Sleep(1 * time.Second)
    fmt.Println(callCount)

    debouncedFn()

    time.Sleep(1 * time.Second)
    fmt.Println(callCount)

    // Output:
    // 1
    // 2
}
```

### <span id="Delay">Delay</span>

<p>Invoke function after delayed time.</p>

<b>Signature:</b>

```go
func Delay(delay time.Duration, fn interface{}, args ...interface{})
```

<b>Example:</b>

```go
package main

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

func main() {
    var print = func(s string) {
        fmt.Println(count) //test delay
    }
    function.Delay(2*time.Second, print, "test delay")
}
```

### <span id="Throttle">Throttle</span>

<p>Creates a throttled version of the provided function. The returned function guarantees that it will only be invoked at most once per interval.</p>

<b>Signature:</b>

```go
func Throttle(fn func(), interval time.Duration) func()
```

<b>Example:</b>

```go
package main

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

func main() {
    callCount := 0

    fn := func() {
        callCount++
    }

    throttledFn := function.Throttle(fn, 1*time.Second)

    for i := 0; i < 5; i++ {
        throttledFn()
    }

    time.Sleep(1 * time.Second)

    fmt.Println(callCount)

    // Output:
    // 1
}
```

### <span id="Schedule">Schedule</span>

<p>Invoke function every duration time, until close the returned bool chan.</p>

<b>Signature:</b>

```go
func Schedule(d time.Duration, fn interface{}, args ...interface{}) chan bool
```

<b>Example:</b>

```go
package main

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

func main() {
    var res []string
    appendStr := func(s string) {
        res = append(res, s)
    }

    stop := function.Schedule(1*time.Second, appendStr, "*")
    time.Sleep(5 * time.Second)
    close(stop)

    fmt.Println(res) //[* * * * *]
}
```

### <span id="Pipeline">Pipeline</span>

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

<b>Signature:</b>

```go
func Pipeline(funcs ...func(interface{}) interface{}) func(interface{}) interface{}
```

<b>Example:</b>

```go
package main

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

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

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

    result := fn(2)

    fmt.Println(result)

    // Output:
    // 36
}
```

### <span id="Watcher">Watcher</span>

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

<b>Signature:</b>

```go
type Watcher struct {
    startTime int64
    stopTime  int64
    excuting  bool
}
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
```

<b>Example:</b>

```go
package main

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

func main() {
    w := &function.Watcher{}
    w.Start()

    longRunningTask()

    fmt.Println(w.excuting) //true

    w.Stop()

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

    w.Reset()

    fmt.Println(w.excuting) //false

    fmt.Println(w.startTime) //0
    fmt.Println(w.stopTime) //0
}

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

```