I love auto-layout in iOS, which is, indeed, a constraint system. It is not easy to get the hang of it, but once one does, it is extremely powerful and delightful to use.

I legitimately find myself wishing I had access to this any time I have to build UI in other languages.

I remember being so skeptical and annoyed when first using it but over the years I became sold on it. It’s the only system I’ve used where I could come back years down the road and figuring out the layout was still straightforward enough debugging wise.