英文:
How to define the key of context in go
问题
为什么一般定义是
type key int
type userKey key
而不是
type userKey int
使用第一种方式有什么好处？
我看到官方文档中没有解释
然后我看到每个人都在使用第一种方式
英文:
Why is the general definition of
type key int
type userKey key
instead of
type userKey int
What are the benefits of using the first one?
I see that there is no explanation in the official documentation
Then I see that everyone is using the first
答案1
得分: 2
type <name> <anothertype> 创建一个类型，其内存布局与 anothertype 相同，但没有其方法。
这样可以在一个本来不可能的类型上声明方法。
例如，使用 type key int 可以在 key 上实现 fmt.Stringer，
type key int
func (k key) String() string {
return fmt.Sprintf("Value of key is %d", k)
}
可以这样使用：
func (k key) String() string {
return fmt.Sprintf("Value of key is %d", k)
}
func main() {
var k key = 20
fmt.Printf("k: %v\n", k) // k: Value of key is 20
var intK int = 10
fmt.Printf("intK: %v\n", intK) //intK: 10
}
英文:
type <name> <anothertype> creates a type whose memory layout is same as anothertype but does not have its methods.
This allows to declare methods on a type that otherwise would not be possible.
e.g. with type key int it is possible to implement fmt.Stringer with key,
type key int
func (k key) String() string {
return fmt.Sprintf("Value of key is %d", k)
}
which can be used as
func (k key) String() string {
return fmt.Sprintf("Value of key is %d", k)
}
func main() {
var k key = 20
fmt.Printf("k: %v\n", k) // k: Value of key is 20
var intK int = 10
fmt.Printf("intK: %v\n", intK) //intK: 10
}
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