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billzhuang

请教一个函数返回函数的语法

  •  
  •   billzhuang
    billzhuang Dec 20, 2022 2834 views
    This topic created in 1227 days ago, the information mentioned may be changed or developed.

    https://go.dev/play/p/xgmb2tPtMfw

    package main import ( "fmt" "time" ) func main() { // incorrect abc := time.Now().UTC fmt.Println(abc()) time.Sleep(1000000000) fmt.Println(abc()) fmt.Println("-------------------------------") // correct bcd := time.Now fmt.Println(bcd()) time.Sleep(1000000000) fmt.Println(bcd()) } 

    上面那种写法,返回的是固定值,编译器优化?

    如果我不想自定义一个函数,类似

    func utc() time.Time { return time.Now().UTC() } abc := utc ... 

    或者匿名函数,类似

    abc := func() time.Time { return time.Now().UTC()} 

    我就想直接 inline 定义这个匿名函数,咋整?

    谢谢。

    7 replies    2022-12-20 21:56:55 +08:00
    yaott2020
        1
    yaott2020  
       Dec 20, 2022 via Android
    incorrect 你已经把 time.Now()执行了,结果都出来了,后面那个 UTC 函数只是转换而已。因此结果就是固定的
    billzhuang
        2
    billzhuang  
    OP
       Dec 20, 2022
    @yaott2020 对。那我该怎么让 go 延迟执行这个 time.Now()呢?
    koebehshian
        4
    koebehshian  
       Dec 20, 2022   1
    函数返回函数
    ```
    // You can edit this code!
    // Click here and start typing.
    package main

    import (
    "fmt"
    "time"
    )

    func returnTimeFunc() func() time.Time {
    return time.Now
    }
    func main() {

    // correct
    bcd := returnTimeFunc()
    fmt.Println(bcd())

    }
    ```
    SorcererXW
        5
    SorcererXW  
       Dec 20, 2022   1
    abc : = time.Time.UTC

    fmt.Println(abd(time.Now()))
    GeruzoniAnsasu
        6
    GeruzoniAnsasu  
       Dec 20, 2022   1
    golang 中的 func 是一等公民( first-class )


    bcd := func() func() time.Time { return time.Now }
    bcd_ := bcd()
    fmt.Println(bcd_())

    fmt.Println(func() time.Time { return time.Now() }())

    都是可以的
    billzhuang
        7
    billzhuang  
    OP
       Dec 20, 2022 via iPhone
    谢谢各位,我懂了。
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