[Draft] Throwing Properties and Subscripts

[Lantua]

@DevAndArtist

I might miss something from the modify thread but why is it a problem?

Nothing is wrong really. Though I'd feel weird if the Unit is introduced solely for this usage.

And if we're to change the set semantic we might as well do that. If I interpret @John_McCall's post here correctly, that may not be off the table. Though after re-reading it, I could be totally off the mark there .

@technogen

Wait, why would it be source breaking when the behavior is only present in throwing setters, which are purely additive?

I mean that we can either introduce set throws with different semantic and be inconsistent with set, or retroactively change set semantic which is source breaking (or do something else).

@technogen

Given a non-throwing settable property, what happens if a mutating method throws? Is the setter called? If so, what is the newValue equal to?

The setter is called with the value being whatever it is right before the throw happens.