Thank you for the help @Axel Wagner
On Tuesday, 28 February 2023 at 18:20:54 UTC Axel Wagner wrote:
> You are running into this: https://go.dev/doc/faq#covariant_types
>
> > How could I do that?
>
> You probably have to write a wrapper. Or change the concrete type to
> return an interface. Or test using the concrete type, instead of using
> mocks.
>
> On Tue, Feb 28, 2023 at 6:08 PM Rick Schubert
> wrote:
>
>> I am having a question about how to implement interfaces correctly in Go
>> when it comes to third-party packages that use chained methods. I have
>> compiled an example project below for you so that you can understand the
>> problem.
>>
>>
>> package main
>>
>> import (
>> myAPI "github.com/hashicorp/vault/api"
>> )
>>
>> var myClient *myAPI.Client
>>
>> type MyProvider interface {
>> GetClient() MyAPIClient
>> }
>>
>> type MyAPIClient interface {
>> // I want to do this but it does not work
>> Logical() MyAPILogical
>> // This works though
>> // Logical() *myAPI.Logical
>> }
>>
>> type MyAPILogical interface {
>> Write(path string, data map[string]interface{}) (*myAPI.Secret, error)
>> }
>>
>> type Provider struct {}
>>
>> func PublicFunctionIWantToTest(provider MyProvider) {
>> client := provider.GetClient()
>> // We normally do something here with the 'client' variable, but important
>> // is that we forward it later on
>> privateFunctionThatIsUsedInTheTest(client)
>> }
>>
>> func privateFunctionThatIsUsedInTheTest(client MyAPIClient)
>> (*myAPI.Secret, error) {
>> return client.Logical().Write(
>> "/here/goes/some/path",
>> map[string]interface{}{
>> "key": "value",
>> },
>> )
>> }
>>
>> func NewProvider() MyProvider {
>> return Provider{}
>> }
>>
>> func (p Provider) GetClient() MyAPIClient {
>> return myClient
>> }
>>
>> // Empty function just so that this example can be built
>> func main() {}
>>
>>
>> As you can see, the package has a chained method Logical().Write() .
>> Since I want to create tests for PublicFunctionIWantToTest, I want to
>> pass down all the functionality as interface so that I can use
>> https://vektra.github.io/mockery/ to create mocks for it.
>>
>> Unfortunately, I am hitting an issue with my MyAPIClient and the
>> MyAPILogical interface. Since I can see in the package's documentation (
>> https://pkg.go.dev/github.com/hashicorp/vault/a...@v1.8.1#Logical.Write
>> <https://pkg.go.dev/github.com/hashicorp/vault/api@v1.8.1#Logical.Write>)
>> that the Logical() method returns a Logical instance, I want to make it
>> so that interface method returns the other interface MyAPILogical (line
>> 15). This does not work though, there is an error on line 47 in the
>> GetClient() method saying that I would not implement the interface
>> correctly. How could I do that?
>>
>> cannot use myClient (variable of type *api.Client) as MyAPIClient value
>> in return statement: *api.Client does not implement MyAPIClient (wrong type
>> for method Logical)
>> have Logical() *api.Logical
>> want Logical() MyAPILogicalcompilerInvalidIfaceAssign
>>
>> Thank you kindly
>>
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>> .
>>
>
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