英文:
Marshalling Time fields as Unix time
问题
我想将我的time.Time字段编码为数字的Unix时间戳，并且我不想为每个结构体实现自定义的MarshalJSON函数，因为我有很多很多的结构体。
所以，我尝试定义一个类型别名，如下所示：
type Timestamp time.Time
并在其上实现MarshalJSON，如下所示：
func (t Timestamp) MarshalJSON() ([]byte, error) {
return []byte(strconv.FormatInt(t.Unix(), 10)), nil
}
但是这给我一个错误：t.Unix undefined (type Timestamp has no field or method Unix)，这对我来说没有意义。难道Timestamp不应该"继承"（我知道这可能是错误的术语）time.Time的所有函数吗？
我还尝试使用类型断言，如下所示：
strconv.FormatInt(t.(time.Time).Unix(), 10)
但这也失败了，报错说类型断言无效：invalid type assertion: t.(time.Time) (non-interface type Timestamp on left)。
英文:
I want to encode my time.Time fields as numeric Unix time and I would prefer not to implement custom MarshalJSON functions for each and every struct, since I have lots and lots of structs.
So, I tried defining a type alias as such:
type Timestamp time.Time
And implementing MarshalJSON on it like so:
func (t Timestamp) MarshalJSON() ([]byte, error) {
return []byte(strconv.FormatInt(t.Unix(), 10)), nil
}
But that gives me a t.Unix undefined (type Timestamp has no field or method Unix), which doesn't make sense to me. Shouldn't Timestamp 'inherit' (I know that's probably the wrong term) all functions of time.Time?
I also tried using a type assertion like so:
strconv.FormatInt(t.(time.Time).Unix(), 10)
But that also fails, complaining about an invalid type assertion: invalid type assertion: t.(time.Time) (non-interface type Timestamp on left)
答案1
得分: 1
你需要将类型转换回time.Time，以便访问其方法。命名类型不会“继承”其基础类型的方法（要实现这一点，你需要使用嵌入）。
func (t Timestamp) MarshalJSON() ([]byte, error) {
return []byte(strconv.FormatInt(time.Time(t).Unix(), 10)), nil
}
另外，就个人偏好而言，我更倾向于使用fmt.Sprintf("%v", i)而不是strconv.FormatInt(i, 10)或者strconv.Itoa(i)。老实说，我不确定哪个更快，但是fmt版本在阅读上更容易理解，就我个人而言。
英文:
You need to convert your type back to a time.Time to have access to its methods. Named types do not "inherit" the methods of their underlying types (to do that, you need embedding).
func (t Timestamp) MarshalJSON() ([]byte, error) {
return []byte(strconv.FormatInt(time.Time(t).Unix(), 10)), nil
}
Also, just as a matter of personal preference, I tend to preferred fmt.Sprintf("%v", i) over strconv.FormatInt(i, 10) or even strconv.Itoa(i). Honestly not sure which is faster, but the fmt version seems easier to read, personally.
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