I understand a bit a go and to certain extend understand interface as well(like how I do ducktyping in ruby) But reading the interface definition https://github.com/golang/go/wiki/CodeReviewComments
I'm clueless what is trying to convey.
1st: I did not understood the comment.
Go interfaces generally belong in the package that uses values of the interface type, not the package that implements those values.
2nd: I do not understand this
Do not define interfaces on the implementor side of an API "for mocking"; instead, design the API so that it can be tested using the public API of the real implementation.
3rd: I do not understand the example
Do not define interfaces before they are used: without a realistic example of usage, it is too difficult to see whether an interface is even necessary, let alone what methods it ought to contain.
package consumer // consumer.go
type Thinger interface { Thing() bool }
func Foo(t Thinger) string { ..... }
package consumer // consumer_test.go
type fakeThinger struct{ … }
func (t fakeThinger) Thing() bool { … }
if Foo(fakeThinger{…}) == "x" { ... }
// DO NOT DO IT!!!
package producer
type Thinger interface { Thing() bool }
type defaultThinger struct{ … }
func (t defaultThinger) Thing() bool { … }
func NewThinger() Thinger { return defaultThinger{ … } }
package producer
type Thinger struct{ … }
func (t Thinger) Thing() bool { … }
func NewThinger() Thinger { return Thinger{ … } }
Can someone explain in plain and easier word the 3 things above.