I currently have code like this: ``` override fun onReject(token: String) { if (savedCon...

# announcements

[Ellen Spertus]

I currently have code like this:

override fun onReject(token: String) {
        if (savedConnectionState is ConnectionState.Authenticating) {
          // do something
        } else {
           // complain
        }
    }
    
    override fun onSend(message: String) {
        if (savedConnectionState is ConnectionState.ReadyToSend) {
            // do something
        } else {
            // complain
        }
    }

Is there a way to create a check() method that takes a type (e.g., ConnectionState.Authenticating) as an argument and tests whether the instance variable savedConnectionState is that type?

[Pavlo Liapota]

Something like this maybe https://pl.kotl.in/4eS7G-xbb ?

[Ellen Spertus]

Nice!

[Ellen Spertus]

(first-place medal for first-class types)

[Ellen Spertus]

I modified your code to return the instance variable as the desired type. https://pl.kotl.in/cDt1J3zpr

[Pavlo Liapota]

Instead of

if (savedState is T) (savedState as T) else null

you can just write

savedState as? T

🙂

[Ellen Spertus]

Thank you. As you can tell from the long variable names, I come from Java.

[Ellen Spertus]

I’ll be adding some sort of error reporting in the else branch so I think I’ll leave it as an else (unless you have a better idea).

[Ellen Spertus]

I hope you don’t mind I looked you up on the interwebz. My grandfather went to college in Kharkiv about 100 years ago. I don’t think they taught functional programming then.

[Ellen Spertus]

Actually, I should probably use the Elvis operator, not if.

[Pavlo Liapota]

My grandfather went to college in Kharkiv about 100 years ago.

Nice 🙂

[Pavlo Liapota]

Actually, I should probably use the Elvis operator, not if.

Sure, whatever is easier in your case.

[Ellen Spertus]

This is pretty ugly:

inline fun <reified T : ConnectionState> check() =
        savedConnectionState as? T ?: {
            Logger.error("savedConnectionState was $savedConnectionState, expected $T")
            null
        }()

[Ellen Spertus]

Is there a way to include T in my error message or does the type get erased?

[Ellen Spertus]

nm, I found the answer

[Pavlo Liapota]

You can write

= (savedConnectionState as? T).also {
    it ?: Logger.error("savedConnectionState was ${savedConnectionState::class}, expected ${T::class}")
}

Or if check

= (savedConnectionState as? T).also {
    if (it == null) Logger.error("...")
}

[Ellen Spertus]

I really appreciate the Kotlin lesson. I’ve never used also before. That’s much more elegant.

[Pavlo Liapota]

let, apply, also and run are amazing 🙂

[Ellen Spertus]

Would you like to be credited in the commit message? I’m coding for Mozilla.

[Pavlo Liapota]

That would be very sweet 😊

[Ellen Spertus]

Let me know if you ever want a referral to Mozilla (or to Google, where my husband works).

[Pavlo Liapota]

Thank you, I appreciate that.