How can I restrict value of variables in Golang?

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英文:

How can I restrict value of variables in Golang?

问题

我知道Go语言中没有setter和getter的惯用方式。但是我需要在Go中限制变量的值。

我定义了一个新类型：

  1. type MyNewStringType string

需要限制值的变量被定义为MyStringType类型。

MyStringType类型的变量只能有三个值："Yes"、"No"、"I don't know"。

在Golang中，我该如何实现呢？
在Java和C++中，我可以使用setter和getter，但在Golang中不太一样。

我知道，我可以创建以下结构体：

  1. type MyNewStringType struct {
  2.    Variable string
  3. }

然后创建以下函数：

  1. func (m *MyNewStringType) SetVariable(newVar string) error {
  2.   if newVar == "Yes" || newVar == "No" || newVar == "I don't know" {
  3.     m.Variable = newVar
  4.     return nil
  5.   } else {
  6.     return errors.New("Wrong value")
  7.   }
  8. }

但我认为这种方式不太对。

英文:

I know Go idiomatic don't have setter and getter. But I need to restrict value of variables in Go.

I defined new type

  1. type MyNewStringType string

And variables, that was defined as MyStringType, need to restrict value.

Variables of MyStringType can have only 3 values:
"Yes", "No", "I don't know"

How can I do it in Golang?
In Java, C++ I have setter and getter, but in Golang is not normal.

I know, I can create

  1. type MyNewStringType struct {
  2.    Variable string
  3. }

and create

  1. func(m *MyNewStringType) SetVariable(newVar string) error {
  2.   if newVar == "Yes" || newVar == "No" || newVar == "I don't know" {
  3.     m.Variable = newVar
  4.     return nil
  5.   } else {
  6.     return errors.New("Wrong value")
  7.   }

But I think it's wrong way.

答案1

得分: 0

这个更好的实现方式可以是允许任何值，并在使用该值时进行验证。以下是一个简短的示例：

  1. package main
  3. import (
  4.   "fmt"
  5.   "os"
  6. )
  8. func main() {
  9.   fmt.Println("第一次尝试")
  10.   if err := doSomething("foo"); err != nil {
  11.     fmt.Fprintf(os.Stderr, "%v\n", err)
  12.   }
  14.   fmt.Println()
  16.   fmt.Println("第二次尝试")
  17.   if err := doSomething("Yes"); err != nil {
  18.     fmt.Fprintf(os.Stderr, "%v\n", err)
  19.   }
  20. }
  22. func doSomething(s string) error {
  23.   switch s {
  24.   case "Yes", "No", "I don't know":
  25.     fmt.Println("成功！")
  26.     return nil
  27.   default:
  28.     return fmt.Errorf("不支持的值：%q", s)
  29.   }
  30. }

输出结果：

  1. 第一次尝试
  2. 不支持的值："foo"
  4. 第二次尝试
  5. 成功！
  7. [代码链接](https://play.golang.org/p/nt8J9wdlZkp)
  9. 如果你坚持按照你提出的方式实现，也许你的`SetVariable`方法会变得更整洁一些，就像上面的示例中使用`switch`语句一样。
  11. <details>
  12. <summary>英文:</summary>
  14. A nicer way of implementing this could be to allow any value, and then validating when the value is used. A short example:
  16.     package main
  18.     import (
  19.       &quot;fmt&quot;
  20.       &quot;os&quot;
  21.     )
  23.     func main() {
  24.       fmt.Println(&quot;First try&quot;)
  25.       if err := doSomething(&quot;foo&quot;); err != nil {
  26.         fmt.Fprintf(os.Stderr, &quot;%v\n&quot;, err)
  27.       }
  29.       fmt.Println()
  31.       fmt.Println(&quot;Second try&quot;)
  32.       if err := doSomething(&quot;Yes&quot;); err != nil {
  33.         fmt.Fprintf(os.Stderr, &quot;%v\n&quot;, err)
  34.       }
  35.     }
  37.     func doSomething(s string) error {
  38.       switch s {
  39.       case &quot;Yes&quot;, &quot;No&quot;, &quot;I don&#39;t know&quot;:
  40.         fmt.Println(&quot;Success!&quot;)
  41.         return nil
  42.       default:
  43.         return fmt.Errorf(&quot;unsupported value: %q&quot;, s)
  44.       }
  45.     }
  47. Output:
  49.     First try
  50.     unsupported value: &quot;foo&quot;
  51.     
  52.     Second try
  53.     Success!
  55. https://play.golang.org/p/nt8J9wdlZkp
  57. If you insist on implementing it in the way you suggest, perhaps your `SetVariable` method would become a little bit tidier if you used a `switch` statement as in the above example.
  59. </details>
  63. # 答案2
  64. **得分**: -5
  66. 翻译结果：
  68. 简短回答：
  70.     type MyString string
  71.     const (
  72.         YES MyString = "yes"
  73.         NO = "no"
  74.         DONTKNOW = "i dont know"
  75.     )
  77.     func foo(arg MyString){
  78.         fmt.Print(arg)
  79.     }
  81.     foo(YES) //成功，输出"yes"
  83.     foo("jop") //编译失败
  85. <details>
  86. <summary>英文:</summary>
  88. Short awnser:
  90.     type MyString string
  91.     const (
  92.         YES MyString = &quot;yes&quot;
  93.         NO = &quot;no&quot;
  94.         DONTKNOW = &quot;i dont know&quot;
  95.     )
  97.     func foo(arg MyString){
  98.         fmt.Print(arg)
  99.     }
  101.     foo(YES) //success, prints &quot;yes&quot;
  103.     foo(&quot;jop&quot;) //fails to compile
  105. </details>

huangapple
  • 本文由 发表于 2016年11月9日 18:02:47
  • 转载请务必保留本文链接：https://go.coder-hub.com/40504253.html
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