Alias Type Definitions do not Inherit Underlying Type Methods
Evan Hicks
—The Problem
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)
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:
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
- SentryGo Error Tracking and Performance Monitoring
- Syntax.fmListen to the Syntax Podcast
- Listen to the Syntax Podcast
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