What could be a good way for provide a compile tim...

# announcements

[Davide Giuseppe Farella]

What could be a good way for provide a compile time - type safety on Any?
Let’s say that I got this class and I want the better way for ensure that image is Drawable, Int, Bitmap, File, String or Uri and placeholder is Drawable, Int, Bitmap or File without crashing at runtime

[LeoColman]

The only way to be safe on type is to use the correct type

[LeoColman]

I don't think there's any sort of structure to guarantee what you want

[LeoColman]

Perhaps with annotation processing

[Davide Giuseppe Farella]

So I should go for some “extra route” like lint or annotation processor, right?

[streetsofboston]

What about creating a sealed class for this (eg ImageResource), where each of its subclasses is wrapping either a Drawablenor an Int, ...or a Uri?

Instead of Any?, you would use ImageResource?.

[Davide Giuseppe Farella]

I guess this is the most easy-typesafe solution, but I would like to avoid the wrapping. Something like androidx.annotation.DrawableRes would be great

[LeoColman]

What is the issue with wrapping?

[LeoColman]

I think the main point here is that you're trying to escape the type system a little bit, and I don't really understood why

[Davide Giuseppe Farella]

This

imageLoader {
    image = item.image
    placeHolder = item.imagePlaceHolder
    target = tvChannelImage
}

would become this:

imageLoader {
    image = ImageResource( item.image )
    placeHolder = ImageResource( item.imagePlaceHolder )
    target = tvChannelImage
}

which I don’t like 🙂

[Davide Giuseppe Farella]

you’re trying to escape the type system a little bit, and I don’t really understood why

Who don’t like to break the rules? 😄

[ghedeon]

Wrapping has another advantage: it can accept params. If your drawable is an Int, let say a vector drawable that needs to be of different color, then you need to provide a color filter, along the Int.

[ghedeon]

for what it's worth, you can have extension functions in these types (with annotated receiver maybe): item.image.toRes()

[Davide Giuseppe Farella]

In that case I would prefer to have imageDrawable, imageBitmap, etc and add some boilerplate to the Builder

[Paul Woitaschek]

Well you can just use a function instead of a property and overload it with all types

[tseisel]

If the only issue you have with wrapping is the readability of the DSL syntax, you can define extension properties on your builder, so that there is a property for each supported type :

inline var Builder.imageDrawableRes: Int
    get() = throw Exception("No getter here")
    set(value) = this.image = DrawableResource(value)

You can then use it in the DSL like this :

imageLoader {
    imageDrawableRes = R.drawable.my_awesome_image
}

[Davide Giuseppe Farella]

@tseisel yes thanks, I tough at something like that a couple of messages above 👍