Pointers for range循环中指针和值片之间的差异

请检查此代码段：

package main

import (  
    "fmt"
    "time"
)

type field struct {  
    name string
}

func (p *field) print() {  
    fmt.Println(p.name)
}

func main() {
    fmt.Println("use values:")

    // use values in range loop and go rountines
    values := []field{{"one"},{"two"},{"three"}}
    for _, v := range values {
        go v.print()
    }

    time.Sleep(time.Second)

    fmt.Println()
    fmt.Println("use pointers:")

    // use pointers in range loop and go rountines
    poniters := []*field{{"one"},{"two"},{"three"}}
    for _, v := range poniters {
        go v.print()
    }

    time.Sleep(time.Second)
}

链接此处：

上面的代码将检查for循环中指针和值之间的差异，同时也使用go语句。代码：

values := []field{{"one"},{"two"},{"three"}}
for _, v := range values {
    go v.print()
}

我们知道控制台将打印three，因为for循环在goroutines开始执行之前运行到它的末尾，goroutines将v写入片的最后一个元素。但是指针呢

poniters := []*field{{"one"},{"two"},{"three"}}
for _, v := range poniters {
    go v.print()
}

它似乎在打印一二三，为什么

---

谢谢。

A：在调用函数之前会对参数进行评估。求值后，调用的参数按值传递给函数，被调用函数开始执行，因此：

第一个

go v.print（）
第二个
go v.print（）

如果
的第一个
循环在goroutines开始之前完成，
&v
对于调用是相同的，并且这三个调用都是相同的。参见代码2，将
time.Sleep（100）
添加到第一个循环的
go v.print（）
之后。或者使用
go func（v字段）{v.print（）}（v）
on.

此外，这里还有数据竞赛（参见B）

对于第二个
go（*字段），print（v）
这里
v
是指针，在调用
print
和之前计算了三个goroutines参数，它们有三个不同的地址

1-试试这个：

输出：

use values:
&{one}
&{two}
&{three}
three
three
three

use pointers:
&{one}
&{two}
&{three}
two
one
three

use values:
&{one}
one
&{two}
two
&{three}
three

use pointers:
&{one}
&{two}
&{three}
one
two
three

use values:
==================
WARNING: DATA RACE
Read at 0x00c042030210 by goroutine 6:
  runtime.convT2E()
      Go/src/runtime/iface.go:155 +0x0
  main.(*field).print()
      .../m.go:14 +0x6c

Previous write at 0x00c042030210 by main goroutine:
  main.main()
      .../m.go:22 +0x1c3

Goroutine 6 (running) created at:
  main.main()
      .../m.go:23 +0x204
==================
two
three
three

use pointers:
one
two
three
Found 1 data race(s)


2-试试这个：

输出：

use values:
&{one}
&{two}
&{three}
three
three
three

use pointers:
&{one}
&{two}
&{three}
two
one
three

use values:
&{one}
one
&{two}
two
&{three}
three

use pointers:
&{one}
&{two}
&{three}
one
two
three

use values:
==================
WARNING: DATA RACE
Read at 0x00c042030210 by goroutine 6:
  runtime.convT2E()
      Go/src/runtime/iface.go:155 +0x0
  main.(*field).print()
      .../m.go:14 +0x6c

Previous write at 0x00c042030210 by main goroutine:
  main.main()
      .../m.go:22 +0x1c3

Goroutine 6 (running) created at:
  main.main()
      .../m.go:23 +0x204
==================
two
three
three

use pointers:
one
two
three
Found 1 data race(s)


B:您有数据竞争，请尝试
go build-race
，然后运行生成的文件，
警告：数据竞争
：

输出：

use values:
&{one}
&{two}
&{three}
three
three
three

use pointers:
&{one}
&{two}
&{three}
two
one
three

use values:
&{one}
one
&{two}
two
&{three}
three

use pointers:
&{one}
&{two}
&{three}
one
two
three

use values:
==================
WARNING: DATA RACE
Read at 0x00c042030210 by goroutine 6:
  runtime.convT2E()
      Go/src/runtime/iface.go:155 +0x0
  main.(*field).print()
      .../m.go:14 +0x6c

Previous write at 0x00c042030210 by main goroutine:
  main.main()
      .../m.go:22 +0x1c3

Goroutine 6 (running) created at:
  main.main()
      .../m.go:23 +0x204
==================
two
three
three

use pointers:
one
two
three
Found 1 data race(s)