Unresolved type in pointer receiver

Question

I have type Process in a library called lib.

I am trying to import that library and add a method associated with type from lib package.

func(p *lib.Process) DoSomething(pp *lib.Process) 

But I have an error unresolved type 'lib' inside of func(...). It ls surprising for me, because there is no error inside DoSomething.

How is it possible to overcome it?

Answer 1

You cannot extend types defined in other packages. What you can do, is embed a type in another package in your own type, then extend your own type. Example:

type MyProcess struct {
    lib.Process
}

func (p *MyProcess) DoSomething(...) {
    // ...
}

With this method, all of the existing methods on lib.Process will still be accessible, as well as your own.

Answer 2

You can't extend existing types in another package. You can define your own type or sub-package as follows.

type LibProcess lib.Process

func(p *LibProcess)DoSomething(pp *LibProcess) {}

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type alias vs defintion

type LibProcess lib.Process // type defintion

type LibProcess = lib.Process // type alias

• A type definition creates a new, distinct type with the same underlying type and operations as the given type, and binds an identifier to it.

• An alias declaration binds an identifier to the given type.