在Go语言中有foreach循环吗？

huangapple
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英文:

Is there a foreach loop in Go?

问题

在Go语言中有foreach结构吗？我可以使用for循环遍历切片或数组吗？

英文:

Is there a foreach construct in the Go language?
Can I iterate over a slice or array using a for?

答案1

得分: 1103

从*带有range子句的for语句*：

> 带有“range”子句的“for”语句遍历数组、切片、字符串或映射的所有条目，或在通道上接收的值。
> 对于每个条目，它将迭代值分配给相应的迭代变量，然后执行代码块。

例如：

<!-- language: lang-golang -->

  1. for index, element := range someSlice {
  2.     // index是我们所在的索引
  3.     // element是someSlice中我们所在位置的元素
  4. }

如果您不关心索引，可以使用_：

<!-- language: lang-golang -->

  1. for _, element := range someSlice {
  2.     // element是someSlice中我们所在位置的元素
  3. }

下划线_是空白标识符，一个匿名占位符。

英文:

From For statements with range clause:

> A "for" statement with a "range" clause iterates through all entries
> of an array, slice, string or map, or values received on a channel.
> For each entry it assigns iteration values to corresponding iteration
> variables and then executes the block.

As an example:

<!-- language: lang-golang -->

  1. for index, element := range someSlice {
  2.     // index is the index where we are
  3.     // element is the element from someSlice for where we are
  4. }

If you don't care about the index, you can use _:

<!-- language: lang-golang -->

  1. for _, element := range someSlice {
  2.     // element is the element from someSlice for where we are
  3. }

The underscore, _, is the blank identifier, an anonymous placeholder.

答案2

得分: 224

Go有一种类似于foreach的语法。它支持数组/切片、映射和通道。

遍历数组或切片：

  1. // 索引和值
  2. for i, v := range slice {}
  4. // 仅索引
  5. for i := range slice {}
  7. // 仅值
  8. for _, v := range slice {}

遍历映射：

  1. // 键和值
  2. for key, value := range theMap {}
  4. // 仅键
  5. for key := range theMap {}
  7. // 仅值
  8. for _, value := range theMap {}

遍历通道：

  1. for v := range theChan {}

遍历通道等同于从通道接收数据，直到通道关闭：

  1. for {
  2.     v, ok := &lt;-theChan
  3.     if !ok {
  4.         break
  5.     }
  6. }
英文:

Go has a foreach-like syntax. It supports arrays/slices, maps and channels.

Iterate over an array or a slice:

  1. // index and value
  2. for i, v := range slice {}
  4. // index only
  5. for i := range slice {}
  7. // value only
  8. for _, v := range slice {}

Iterate over a map:

  1. // key and value
  2. for key, value := range theMap {}
  4. // key only
  5. for key := range theMap {}
  7. // value only
  8. for _, value := range theMap {}

Iterate over a channel:

  1. for v := range theChan {}

Iterating over a channel is equivalent to receiving from a channel until it is closed:

  1. for {
  2.     v, ok := &lt;-theChan
  3.     if !ok {
  4.         break
  5.     }
  6. }

答案3

得分: 23

以下是在Go中使用foreach的示例代码：

  1. package main
  3. import (
  4.     "fmt"
  5. )
  7. func main() {
  9.     arrayOne := [3]string{"Apple", "Mango", "Banana"}
  11.     for index, element := range arrayOne {
  13.         fmt.Println(index)
  14.         fmt.Println(element)
  16.     }
  18. }

这是一个运行示例 https://play.golang.org/p/LXptmH4X_0

英文:

Following is the example code for how to use foreach in Go:

  1. package main
  3. import (
  4.     &quot;fmt&quot;
  5. )
  7. func main() {
  9.     arrayOne := [3]string{&quot;Apple&quot;, &quot;Mango&quot;, &quot;Banana&quot;}
  11.     for index,element := range arrayOne{
  13.         fmt.Println(index)
  14.         fmt.Println(element)
  16.     }
  18. }

This is a running example https://play.golang.org/p/LXptmH4X_0

答案4

得分: 14

是的，range：

for 循环的 range 形式可以迭代一个切片或映射。

当迭代一个切片时，每次迭代会返回两个值。第一个是索引，第二个是该索引处元素的副本。

示例：

  1. package main
  3. import "fmt"
  5. var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}
  7. func main() {
  8.     for i, v := range pow {
  9.         fmt.Printf("2**%d = %d\n", i, v)
  10.     }
  12.     for i := range pow {
  13.         pow[i] = 1 << uint(i) // == 2**i
  14.     }
  15.     for _, value := range pow {
  16.         fmt.Printf("%d\n", value)
  17.     }
  18. }
  • 通过将值赋给 _，可以跳过索引或值。
  • 如果只想要索引，完全省略 , 后面的值。
英文:

Yes, range:

The range form of the for loop iterates over a slice or map.

When ranging over a slice, two values are returned for each iteration. The first is the index, and the second is a copy of the element at that index.

Example:

  1. package main
  3. import &quot;fmt&quot;
  5. var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}
  7. func main() {
  8.     for i, v := range pow {
  9.         fmt.Printf(&quot;2**%d = %d\n&quot;, i, v)
  10.     }
  12.     for i := range pow {
  13.         pow[i] = 1 &lt;&lt; uint(i) // == 2**i
  14.     }
  15.     for _, value := range pow {
  16.         fmt.Printf(&quot;%d\n&quot;, value)
  17.     }
  18. }
  • You can skip the index or value by assigning to _.
  • If you only want the index, drop the , value entirely.

答案5

得分: 13

以下示例展示了如何在for循环中使用range运算符来实现foreach循环。

  1. func PrintXml (out io.Writer, value interface{}) error {
  2.     var data []byte
  3.     var err error
  5.     for _, action := range []func() {
  6.         func () { data, err = xml.MarshalIndent(value, "", "  ") },
  7.         func () { _, err = out.Write([]byte(xml.Header)) },
  8.         func () { _, err = out.Write(data) },
  9.         func () { _, err = out.Write([]byte("\n")) }} {
  10.         action();
  11.         if err != nil {
  12.             return err
  13.         }
  14.     }
  15.     return nil;
  16. }

该示例遍历一个函数数组，以统一处理函数的错误。完整示例可在Google的playground中找到。

PS：它还显示了悬挂括号对于代码的可读性是一个不好的主意。提示：for条件在action()调用之前结束。显而易见，不是吗？

英文:

The following example shows how to use the range operator in a for loop to implement a foreach loop.

  1. func PrintXml (out io.Writer, value interface{}) error {
  2.     var data []byte
  3.     var err error
  5.     for _, action := range []func() {
  6.         func () { data, err = xml.MarshalIndent(value, &quot;&quot;, &quot;  &quot;) },
  7.         func () { _, err = out.Write([]byte(xml.Header)) },
  8.         func () { _, err = out.Write(data) },
  9.         func () { _, err = out.Write([]byte(&quot;\n&quot;)) }} {
  10.         action();
  11.         if err != nil {
  12.             return err
  13.         }
  14.     }
  15.     return nil;
  16. }

The example iterates over an array of functions to unify the error handling for the functions. A complete example is at Google´s playground.

PS: it shows also that hanging braces are a bad idea for the readability of code. Hint: the for condition ends just before the action() call. Obvious, isn't it?

答案6

得分: 12

你实际上可以使用range而不引用其返回值，通过对你的类型使用for range：

<!-- language: lang-go -->

  1. arr := make([]uint8, 5)
  2. i,j := 0,0
  3. for range arr {
  4.     fmt.Println("数组循环", i)
  5.     i++
  6. }
  8. for range "bytes" {
  9.     fmt.Println("字符串循环", j)
  10.     j++
  11. }

https://play.golang.org/p/XHrHLbJMEd

英文:

You can in fact use range without referencing its return values by using for range against your type:

<!-- language: lang-go -->

  1. arr := make([]uint8, 5)
  2. i,j := 0,0
  3. for range arr {
  4.     fmt.Println(&quot;Array Loop&quot;, i)
  5.     i++
  6. }
  8. for range &quot;bytes&quot; {
  9.     fmt.Println(&quot;String Loop&quot;, j)
  10.     j++
  11. }

https://play.golang.org/p/XHrHLbJMEd

答案7

得分: 1

这可能很明显，但你可以像这样内联数组：

  1. package main
  3. import (
  4. 	"fmt"
  5. )
  7. func main() {
  8. 	for _, element := range [3]string{"a", "b", "c"} {
  9. 		fmt.Print(element)
  10. 	}
  11. }

输出：

  1. abc

https://play.golang.org/p/gkKgF3y5nmt

英文:

This may be obvious, but you can inline the array like so:

  1. package main
  3. import (
  4. 	&quot;fmt&quot;
  5. )
  7. func main() {
  8. 	for _, element := range [3]string{&quot;a&quot;, &quot;b&quot;, &quot;c&quot;} {
  9. 		fmt.Print(element)
  10. 	}
  11. }

outputs:

  1. abc

https://play.golang.org/p/gkKgF3y5nmt

答案8

得分: 1

我看到很多使用range的例子。提醒一下，range会创建一个迭代对象的副本。如果你在foreach循环中对副本进行更改，那么原始容器中的值不会改变，这种情况下你需要使用传统的for循环，通过索引递增并解引用索引引用。例如：

  1. for i := 0; i < len(arr); i++ {
  2. 	element := &arr[i]
  3. 	element.Val = newVal
  4. }
英文:

I'm seeing a lot of examples using range. Just a heads up that range creates a copy of whatever you're iterating over. If you make changes to the contents in a foreach range you will not be changing the values in the original container, in that case you'll need a traditional for loop with an index you increment and deference indexed reference. E.g.:

  1. for i := 0; i &lt; len(arr); i++ {
  2. 	element := &amp;arr[i]
  3. 	element.Val = newVal
  4. }

答案9

得分: 0

我刚刚实现了这个库：https://github.com/jose78/go-collection。

这是如何使用Foreach循环的示例：

  1. package main
  3. import (
  4.     "fmt"
  6.     col "github.com/jose78/go-collection/collections"
  7. )
  9. type user struct {
  10.     name string
  11.     age  int
  12.     id   int
  13. }
  15. func main() {
  16.     newList := col.ListType{user{"Alvaro", 6, 1}, user{"Sofia", 3, 2}}
  17.     newList = append(newList, user{"Mon", 0, 3})
  19.     newList.Foreach(simpleLoop)
  21.     if err := newList.Foreach(simpleLoopWithError); err != nil{
  22.         fmt.Printf("This error >>> %v <<< was produced", err )
  23.     }
  24. }
  26. var simpleLoop col.FnForeachList = func(mapper interface{}, index int) {
  27.     fmt.Printf("%d.- item:%v\n", index, mapper)
  28. }
  31. var simpleLoopWithError col.FnForeachList = func(mapper interface{}, index int) {
  32.     if index > 1{
  33.         panic(fmt.Sprintf("Error produced with index == %d\n", index))
  34.     }
  35.     fmt.Printf("%d.- item:%v\n", index, mapper)
  36. }

这个执行的结果应该是：

  1. 0.- item:{Alvaro 6 1}
  2. 1.- item:{Sofia 3 2}
  3. 2.- item:{Mon 0 3}
  4. 0.- item:{Alvaro 6 1}
  5. 1.- item:{Sofia 3 2}
  6. Recovered in f Error produced with index == 2
  8. ERROR: Error produced with index == 2
  9. This error >>> Error produced with index == 2 <<< was produced

在playGrounD中尝试这段代码。

英文:

I have just implemented this library: https://github.com/jose78/go-collection.

This is an example of how to use the Foreach loop:

  1. package main
  3. import (
  4.     &quot;fmt&quot;
  6.     col &quot;github.com/jose78/go-collection/collections&quot;
  7. )
  9. type user struct {
  10.     name string
  11.     age  int
  12.     id   int
  13. }
  15. func main() {
  16.     newList := col.ListType{user{&quot;Alvaro&quot;, 6, 1}, user{&quot;Sofia&quot;, 3, 2}}
  17.     newList = append(newList, user{&quot;Mon&quot;, 0, 3})
  19.     newList.Foreach(simpleLoop)
  21.     if err := newList.Foreach(simpleLoopWithError); err != nil{
  22.         fmt.Printf(&quot;This error &gt;&gt;&gt; %v &lt;&lt;&lt; was produced&quot;, err )
  23.     }
  24. }
  26. var simpleLoop col.FnForeachList = func(mapper interface{}, index int) {
  27.     fmt.Printf(&quot;%d.- item:%v\n&quot;, index, mapper)
  28. }
  31. var simpleLoopWithError col.FnForeachList = func(mapper interface{}, index int) {
  32.     if index &gt; 1{
  33.         panic(fmt.Sprintf(&quot;Error produced with index == %d\n&quot;, index))
  34.     }
  35.     fmt.Printf(&quot;%d.- item:%v\n&quot;, index, mapper)
  36. }

The result of this execution should be:

  1. 0.- item:{Alvaro 6 1}
  2. 1.- item:{Sofia 3 2}
  3. 2.- item:{Mon 0 3}
  4. 0.- item:{Alvaro 6 1}
  5. 1.- item:{Sofia 3 2}
  6. Recovered in f Error produced with index == 2
  8. ERROR: Error produced with index == 2
  9. This error &gt;&gt;&gt; Error produced with index == 2
  10.  &lt;&lt;&lt; was produced

Try this code in playGrounD.

huangapple
  • 本文由 发表于 2011年10月16日 12:47:32
  • 转载请务必保留本文链接：https://go.coder-hub.com/7782411.html
  • foreach
  • go
  • slice
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