Hi, anyone knows how I can make the following snip...

# codereview

[louiscad]

Hi, anyone knows how I can make the following snippet more safe?

/** Matches [android.support.v7.app.AppCompatViewInflater.createView] content. */
val appCompatViewFactory = { clazz: Class<out View>, context: Context, _: Style<out View>? ->
    when (clazz) {
        TextView::class.java -> AppCompatTextView(context)
        Button::class.java -> AppCompatButton(context)
        ImageView::class.java -> AppCompatImageView(context)
        EditText::class.java -> AppCompatEditText(context)
        ...
        else -> null
    }
}

The issue is that there's no type check, I could return anything for anytype and the compiler won't fail. I want to make sure each when branch returns an object of the type of the case on which it matched.

[Andreas Sinz]

there is no way to do that in kotlin

[louiscad]

I think I'll submit an issue. This could definitely be supported in some way

[Andreas Sinz]

how would that work?

[louiscad]

Allowing reification of Class<*> and smartcasting checks on its instances (like TextView::class.java in my example). This would require me to make my function generic to benefit from this.

[arekolek]

would something like this help?

inline fun <reified T : View> factory(clazz: Class<T>, context: Context) = when (clazz) {
    TextView::class.java -> AppCompatTextView(context)
    Button::class.java -> AppCompatButton(context)
    ImageView::class.java -> AppCompatImageView(context)
    EditText::class.java -> AppCompatEditText(context)
    else -> throw RuntimeException()
} as T

[louiscad]

@arekolek Nope because there is no smart cast, which means you can return Any? where a TextView or other specific type was expected

[arekolek]

wouldn’t that fail at the as T point?

[louiscad]

Yes, but it happens at runtime, not compile time, and I already check the type was what was requested in the caller code

[louiscad]

Here's the first issue to allow when on reified types https://youtrack.jetbrains.com/issue/KT-26048

[louiscad]

Here's the second issue to allow reified on non inline functions that have a Class or KClass parameter: https://youtrack.jetbrains.com/issue/KT-26049

[Andreas Sinz]

is TextView the same class that AppCompatTextView returns?

[louiscad]

AppCompatTextView is a TextView

[Andreas Sinz]

ah ok

[Andreas Sinz]

and the second question: How does the reification work on the JVM without inlining?

[louiscad]

By getting the type from the class parameter

[Andreas Sinz]

but at runtime the generic type is removed

[louiscad]

It's passed as a parameter (Class<V>)

[louiscad]

By the way, I found a way to make reified type parameters resuscitate at runtime, it's puzzling me that it can work. I'll post link to the code later