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Alias Type Definitions do not Inherit Underlying Type Methods

Alias Type Definitions do not Inherit Underlying Type Methods

Evan Hicks

—

The ProblemJump To Solution

Type definitions do not inherit underlying type methods.
Compile Error: ./prog.go:17:3: b.Print undefined (type Bar has no field or method Print)

Click to Copy
package main

import (
    "fmt"
)

type Foo struct{}

func (f Foo) Print() {
    fmt.Println("foo")
}

type Bar Foo

func main() {
    b := Bar{}
    b.Print()
}

The Solution

Go does not have traditional inheritance like other languages, therefore the alias type declaration type Bar Foo works differently in Go. When you create a new type based on another type, your new type (Bar) doesn’t inherit the methods from Foo, which is why b.Print is undefined.

The fix:

Click to Copy
package main

import (
    "fmt"
)

type Foo struct{}

func (f Foo) Print() {
    fmt.Println("foo")
}

type Bar struct {
    Foo
}

func main() {
    b := Bar{}
    b.Print()
}

This creates a new type Bar, and embeds it with an implicit Foo object. In this case, when you call a method on a Bar object, it will check to see if Bar has that method, and if it doesn’t, it will check Foo for the method and use that.

Further Reading

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