I don't understand what these lines inside when do...

# android

[Mehdi Haghgoo]

I don't understand what these lines inside when do. Would someone mind explaning a bit to me?

override fun toString(): String {
    return when (this) {
        is Success<*> -> "Success[data=$data]"
        is Error -> "Error[exception=$exception]"
    }
}

This is from the template Login Activity in Android Studio. What is Success<*> and what is "Success[data=$data]"?

[Luke]

Basically, this can be an instance of either Success, or Error. You are checking whether you have an instance of one or the other. The thing is that your class is generic. You can have a Success<Int>, or a Success<String> for example. In this case, you don't care whether you have Int or String, you want to match any Success, hence the wildcard <*>

[Mehdi Haghgoo]

So what is the Success[data...] part?

[Paul Woitaschek]

It returns a string with the datas to string implementation

[Vahalaru]

Success is an array, so saying Success[data=$data] is saying you want the data (the info aka the stuff that is important in the scenario)

[rook]

Just to clarify, success is not an array. That part is just a string whose syntax does not represent the structure of the data.

This appears to be something like a sealed class or some kind of base class. Based on the syntax here, we can tell that this is probably something like

sealed class Result<T>(
    val data: T?
    val exception: Exception?
) {
    class Success<T>(data: T): Result<T>(data, null)
    class Error(exception: Exception): Result<Nothing>(null, exception)
}

Given Success(14).toString() , we can expect an output of Success[data=14].
Given Success("foo").toString(), we can expect an output of Success[data=foo].
Given Error(Exception("foo")), we can expect an output of Error[exception=java.lang.Exception: foo]

The $varName syntax is called string interpolation. it takes the variable supplied, calls the toString function on it, and inserts that string into the string literal that contains it.

Hope that helps @Mehdi Haghgoo

[Mehdi Haghgoo]

Thank you @rook I just saw your reply.