Go方法集 - 指针类型* T与接收者T的调用方法 [英] Go methods sets — Calling method for pointer type *T with receiver T
问题描述
访问规范说:
任何其他类型T的方法集由所有具有接收器类型T的方法组成。相应的指针类型* T的方法集是具有接收器* T或T(即,它也包含T)的方法集。
我理解为:T有自己的方法集,而* T有它拥有方法集合和T的方法集合,因为它可以将接收器* T解引用到T并调用方法。因此,我们可以调用一些接收方T的变量类型T的方法。所以我决定验证我的逻辑:
包主
导入(
fmt
反映
)
$ User $ struct $ {
func(self * User)SayWat(){
fmt.Println(self)
fmt.Println(reflect.TypeOf(self))
fmt.Println(WAT \\\
)
}
func main(){
var user User = User {}
fmt.Println(reflect.TypeOf(user),\\\
)
user.SayWat()
}
http://play.golang.org / p / xMKuLzUbIf
我有点困惑。看起来我可以在T上调用* T的方法吗?我有一个更广泛的示例 http://play.golang.org/p/RROPMj534A ,它也让我困惑。是否有一些反过来类型推断?
我是否缺少某些东西,或者我的逻辑不正确?
谢谢!
您不能在<$ * T
c $ c> T ,但编译器足够聪明,可以为你引用变量,有效地调用
(& user).SayWat()
解释此处:
调用:如果x
(的类型)的方法集包含m,并且参数列表可以分配给
m的参数列表,则方法调用xm()是有效的。如果x是可寻址的并且& x的方法集包含m,则对于(& x).m(),x.m()是简写
。
要理解这种差异,您可以举一个返回值(不可寻址):
func aUser()用户{
返回用户{}
}
...
aUser()。SayWat()
错误:
prog.go:40:不能调用aUser()的指针方法
prog.go:40:不能取aUser
http ://play.golang.org/p/HOTKiiOK7S
Go spec says:
The method set of any other type T consists of all methods with receiver type T. The method set of the corresponding pointer type *T is the set of all methods with receiver *T or T (that is, it also contains the method set of T).
I understand this as: T has its own method set, while *T has it own method set plus the method set of T, because it can dereference receiver *T to T and call the method. Therefore, we can call some method with receiver *T of variable type T.
So I decided to verify my logic:
package main
import (
"fmt"
"reflect"
)
type User struct{}
func (self *User) SayWat() {
fmt.Println(self)
fmt.Println(reflect.TypeOf(self))
fmt.Println("WAT\n")
}
func main() {
var user User = User{}
fmt.Println(reflect.TypeOf(user), "\n")
user.SayWat()
}
http://play.golang.org/p/xMKuLzUbIf
I am a bit confused. It looks like I can call methods "of *T" on T? I have a bit wider example http://play.golang.org/p/RROPMj534A, which confuses me too. Is there some vice versa type inference?
Am I missing something, or my logic is incorrect?
Thanks!
You cannot call a method of *T
on T
, but the compiler is smart enough to take the reference of the variable for you, effectively calling
(&user).SayWat()
This is explained here:
Calls: A method call x.m() is valid if the method set of (the type of) x contains m and the argument list can be assigned to the parameter list of m. If x is addressable and &x's method set contains m, x.m() is shorthand for (&x).m().
To understand the difference, you can for instance take a return value (non-addressable):
func aUser() User {
return User{}
}
...
aUser().SayWat()
Fails with error:
prog.go:40: cannot call pointer method on aUser()
prog.go:40: cannot take the address of aUser()
http://play.golang.org/p/HOTKiiOK7S
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