Go Methods on Pointer Types: Calling Methods with Receiver T for Pointer Type *T

Question:

The Go specification states that the method set of a pointer type T includes the method set of its corresponding type T. Does this mean that we can call methods with receiver T on variables of type T?

Answer:

While the specification suggests this, it is important to note that you cannot directly call methods of *T on T. Instead, the compiler automatically dereferences the variable to &T and invokes the method, effectively executing (&T).m().

This behavior is explicitly defined in the Go specification:

"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(). "

Demonstration:

The following example illustrates this behavior:

package main

import (
    "fmt"
    "reflect"
)

type User struct{}

func (this *User) SayWat() {
    fmt.Println(reflect.TypeOf(this))
    fmt.Println("WAT\n")
}

func main() {
    var user = User{}

    fmt.Println(reflect.TypeOf(user))

    user.SayWat()
}

Despite declaring the SayWat method with a receiver of *User, we can invoke it on user, which is of type User. The compiler automatically handles the dereferencing and calls (&user).SayWat().

Exception:

However, this only applies to addressable variables. If you attempt to call a pointer method on a non-addressable value, you will encounter an error. For instance:

func aUser() User {
    return User{}
}

...

aUser().SayWat() // Error: cannot call pointer method on aUser()