Use case

The most common use-case I think of is when we have a horizontal scrollable in a vertical scrollable. We need to constrain the height of the horizontal one. We can use IntrinsicWidth (which won't work with ListView iirc and is expensive), or we can use SizedBox with height. The latter would be either having a constant height (which usually will be a bad approach as it won't support changes in accessibility text scale) or manually calculating the height from TextPainters and dimension constants in the build.

Proposal

Inspired by the prototypeItem from the ListView, I came up with the idea of having a PrototypeWidth, PrototypeHeight and/or PrototypeSizedBox that would set the dimension(s) of its child to ones that we got from laying out the prototype widget.

With such a widget I could wrap my horizontal ListView with a PrototypeHeight where I pass a list item widget as a prototype.

Execution

I'd be willing to implement such widget, coming up with the API myself or based on your suggestions here :)