Kotlin ENUM classes with common interface implemented by delegates

Question

This is a slightly abstract question about finding a pretty design approach with minimal boilerplate.

Prerequisites:

• I have an ENUM class for enumerating various providers ie: enum class Provider { Google, Microsoft }
• Let's say there is a service interface interface Foo { fun getMail(): Mail } that will be implemented for each specific provider.

I was curious if there is a way to define ENUM class Provider in such way that it's implementing interface Foo and I can later specify by which objects each concrete provider will be implemented?

I wonder if there can be a boilerplate-less way to define enum class of concrete interface while I can later define by which objects concrete provider will be implemented.

Prerequisites aren't solid so if a better design requires changes then I'm eager for a better suggestion.

Answer 1

Yep

You can make the enum implements the interface.

enum class Provider(val mail: Mail) : Foo {
    Google(googleMail),
    Microsoft(microsoftMail);

    override fun getMail(): Mail = mail // Or this.mail
}

interface Foo { fun getMail(): Mail }

Then you access

Provider.Google.getMail()

Other way is using val members

interface Foo { val mail: Mail }

enum class Provider(override val mail: Mail) : Foo {
    Google(googleMail),
    Microsoft(microsoftMail)
}

And access

Provider.Google.mail