is it possible to implement an interface that has private methods?

[Octavian Costache]

Hi everybody,

TL;DR:

Does the presence of a private method on an interface make it impossible to implement that interface outside the package in which it is defined?

Longer story:

This question is not about Gorp, but about implementing an interface that specifies private methods.

We're using Gorp (https://github.com/coopernurse/gorp) as an ORM and so far it's been working out.

But I've gotten to a point where I want to add unittests, and I want to mock out some Gorp functionality.

More precisely I'm trying to create a mock that implements the gorp.SqlExecutor interface which looks kind of like this:

// actual source here https://github.com/coopernurse/gorp/blob/master/gorp.go#L537 

type SqlExecutor interface {

  Get(i interface{}, keys ...interface{}) (interface{}, error)

  Insert(list ...interface{}) error

  Update(list ...interface{}) (int64, error)

  Delete(list ...interface{}) (int64, error)

 

  query(query string, args ...interface{}) (*sql.Rows, error) 

  queryRow(query string, args ...interface{}) *sql.Row

}

 

Notice  the two private methods at the bottom of the interface.

If I try to create a type MockSqlExecutor that implements all the methods in this interface, I get the following error:

go/src/jello/db/db.go:50: cannot use MockSqlExecutor literal (type *MockSqlExecutor) as type gorp.SqlExecutor in assignment:

  *MockSqlExecutor does not implement gorp.SqlExecutor (missing gorp.query method)

Does the presence of a private method on an interface make it impossible to implement that interface outside the package in which it is defined?

Am I missing something here? 

Thanks!
Octavian.

[Dan Kortschak]

Yes, unless you embed the interface in a struct you define.

[Octavian Costache]

Awesome, that's exactly what I was missing! 

Thanks guys!

On Thu, Jul 4, 2013 at 6:25 PM, Islan Dberry <islan...@ymail.com> wrote:

Does the presence of a private method on an interface make it impossible to implement that interface outside the package in which it is defined?

It is possible to implement the interface outside of the package by embedding the interrace. You can mock the exported methods. 

type MockQqlExecutor struct {

   gorp.SqlEecutor

}

func (m *MockSqlExecutor)  Get(i interface{}, keys ...interface{}) (interface{}, error)  { /* your mock impl here */ }

func (m *MockSqlExecutor)  Insert(list ...interface{}) error { /* your mock impl here */ }

func (m *MockSqlExecutor)  Update(list ...interface{})  { /* your mock impl here */ }

func (m *MockSqlExecutor)  Delete(list ...interface{})  { /* your mock impl here */ }

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Octavian Costache · @okvivi

http://vivi.ro