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)
-   [Debounced](#Debounced)
-   [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.</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="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="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))
    }
}

```