CODEWITHSUNDEEP
go
SChang
SChang

Reputation: 1699

Method receivers ambiguity

Working on the go tour today. I noticed that I could pass struct literals to methods associated with pointer to structs, and vice versa. Why is this allowed?

package main

import (
    "fmt"
)

type Vertex struct {
    X, Y float64
}

func (v Vertex) Scale (f float64) {
    v.X = v.X * f
    v.Y = v.Y * f
}

func (v *Vertex) ScaleP(f float64) {
    v.X = v.X * f
    v.Y = v.Y * f
}

func main() {
    v := &Vertex{3, 4}
    vLiteral := Vertex{3, 4}

    v.Scale(5)
    fmt.Println(v)

    v.ScaleP(5)
    fmt.Println(v)

    vLiteral.Scale(5)
    fmt.Println(vLiteral)

    vLiteral.ScaleP(5)
    fmt.Println(vLiteral)
}

Output:

&{3 4}
&{15 20}
{3 4}
{15 20}

Upvotes: 4

Views: 3590

Answers (1)

zzzz
zzzz

Reputation: 91449

See Method sets:

A type may have a method set associated with it (§Interface types, §Method declarations). The method set of an interface type is its interface. 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). Further rules apply to structs containing anonymous fields, as described in the section on struct types. Any other type has an empty method set. In a method set, each method must have a unique method name.

The method set of a type determines the interfaces that the type implements and the methods that can be called using a receiver of that type.

EDIT:

See also 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():

Upvotes: 5

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