推断方法的最佳实践是什么？

huangapple
go评论116阅读模式
英文:

What's the best practice to infer the methods?

问题

我有一个自定义的时间格式，用于正确编码/解码 JSON。然而，每当我需要进行时间计算时，我都需要进行类型转换。这样做是否正确？保持进行类型转换感觉有点丑陋。例如，当我需要“更新”值时，我需要进行两次类型转换（一次转换为时间类型，一次转换为我的类型）。

  1. type Mytime time.Time
  2. var t Mytime
  3. t = Mytime(time.Now())
  4. // 将一个小时添加到我的自定义时间
  5. t = Mytime(time.Time(t).Add(1 * time.Hour))
英文:

I have a custom time format which I use to properly encode/decode json. However whenever I need to do a time computation I need to do a cast. Is this the right way? It feels a bit ugly to keep casting. For example when I need to "update" the value I need to cast it twice ( once to time and once to my type)

  1. type Mytime time.Time
  2. var t Mytime
  3. t = Mytime(time.Now())
  4. // Add an hour to my typed time
  5. t = Mytime(time.Time(t).Add(1 * time.Hour))

答案1

得分: 3

你可以使用嵌入来扩展time.Time类型，例如：

  1. type MyTime struct {
  2.     time.Time
  3. }

然后你可以定义MarshalJSON方法：

  1. func (t MyTime) MarshalJSON() ([]byte, error) {
  2.     // 实现你的逻辑
  3. }

并且仍然可以访问所有time.Time的方法。例如：

  1. t := MyTime{time.Now()}
  2. t.Time = t.Add(time.Hour)

完整示例展示了嵌入和非嵌入自定义时间类型之间的区别。请注意，嵌入仍然不能与期望time.Time值的其他组件透明地进行交互。（这里省略了创建这些类型的原因，例如添加MarshalJSON方法）。

  1. package main
  3. import (
  4.     "fmt"
  5.     "time"
  6. )
  8. type YourTime time.Time
  10. type MyTime struct{ time.Time }
  12. // 一些随机函数，可能在第三方包中，处理time.Time值。
  13. func fn(t time.Time) {
  14.     fmt.Println("fn got:", t)
  15. }
  17. func fn2() time.Time {
  18.     return time.Unix(14e8, 0)
  19. }
  21. func main() {
  22.     var t1 = YourTime(time.Now())
  23.     //t1 = t1.Add(time.Hour)             // 编译错误
  24.     t1 = YourTime(time.Time(t1).Add(time.Hour))
  25.     fmt.Println("ugly t1:", t1)
  26.     fmt.Println("nice t1:", time.Time(t1))
  27.     //fn(t1)                        // 编译错误
  28.     fn(time.Time(t1))
  30.     //t1 = fn2()                    // 编译错误
  31.     t1 = YourTime(fn2())
  33.     var t2 = MyTime{time.Now()}
  34.     // t2 = t2.Add(time.Hour)       // 编译错误
  35.     t2.Time = t2.Add(time.Hour)
  36.     fmt.Println("t2:", t2)
  37.     //fn(t2)                        // 编译错误
  38.     fn(t2.Time)
  40.     //t2 = fn2()                    // 编译错误
  41.     t2.Time = fn2()
  42. }

输出：

  1. ugly t1: {63393494400 0 0x1c9340}
  2. nice t1: 2009-11-11 00:00:00 +0000 UTC
  3. fn got: 2009-11-11 00:00:00 +0000 UTC
  4. t2: 2009-11-10 23:00:00 +0000 UTC
  5. fn got: 2009-11-10 23:00:00 +0000 UTC

你可以在Playground上运行这个示例。

英文:

Presumably you have type Mytime time.Time. If instead you embedded it:

  1. type MyTime struct {
  2.         time.Time
  3. }

Then you could have:

  1. func (t MyTime) MarshalJSON() ([]byte, error) {
  2.         … whatever …
  3. }

and still access all of time.Time's methods.
E.g. something like:

  1.         t := MyType{time.Now()}
  2.         t.Time = t.Add(time.Hour)

Fuller example showing differences between embedded and non-embedded custom time types. Note that embedding still doesn't allow for transparent inter-use with things that expect a time.Time value. (The reason for making these types, e.g. to add a MarshalJSON method has been omitted here).

  1. package main
  3. import (
  4. 	"fmt"
  5. 	"time"
  6. )
  8. type YourTime time.Time
  10. type MyTime struct{ time.Time }
  12. // Some random functions, perhaps in a third party package,
  13. // that deals with time.Time values.
  14. func fn(t time.Time) {
  15. 	fmt.Println("fn got:", t)
  16. }
  18. func fn2() time.Time {
  19. 	return time.Unix(14e8, 0)
  20. }
  22. func main() {
  23. 	var t1 = YourTime(time.Now())
  24. 	//t1 = t1.Add(time.Hour)             // compiler error
  25. 	t1 = YourTime(time.Time(t1).Add(time.Hour))
  26. 	fmt.Println("ugly t1:", t1)
  27. 	fmt.Println("nice t1:", time.Time(t1))
  28. 	//fn(t1)                        // compiler error
  29. 	fn(time.Time(t1))
  31. 	//t1 = fn2()                    // compiler error
  32. 	t1 = YourTime(fn2())
  34. 	var t2 = MyTime{time.Now()}
  35. 	// t2 = t2.Add(time.Hour)       // compiler error
  36. 	t2.Time = t2.Add(time.Hour)
  37. 	fmt.Println("t2:", t2)
  38. 	//fn(t2)                        // compiler error
  39. 	fn(t2.Time)
  41. 	//t2 = fn2()                    // compiler error
  42. 	t2.Time = fn2()
  43. }

<kbd>Playground</kbd>

Output:

  1. ugly t1: {63393494400 0 0x1c9340}
  2. nice t1: 2009-11-11 00:00:00 +0000 UTC
  3. fn got: 2009-11-11 00:00:00 +0000 UTC
  4. t2: 2009-11-10 23:00:00 +0000 UTC
  5. fn got: 2009-11-10 23:00:00 +0000 UTC

huangapple
  • 本文由 发表于 2015年4月2日 02:09:30
  • 转载请务必保留本文链接：https://go.coder-hub.com/29397801.html
  • casting
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