Allow writing to a field of a type in a union

[Memresable]

Suppose the following

Foo :: struct
{
  bar: int,
}
bingo: Maybe(Foo)
fmt.println(bingo.?.bar) // compiles, able to read bar
bingo.?.bar = 10 // doesn't compile, unable to write bar

Currently you can read bar, but you can't write to it, this seems inconsistent to me, I don't know the reason behind not allowing this because it seems like it shouldn't be much of a trouble to do so?

I suppose you're literally just reading part of the union's memory through an offset which isn't that bad? (which I assume that's how reading works here) so what makes it not possible to write to a field then?

[laytan]

The .? construct either panics, or returns a copy of the union value.

So, doing bingo.?.bar = 10 would (if allowed) assign 10 to the copy, which you have no reference to, so that's certainly not something you ever want. This is why it is not allowed.

If you actually want to assign 10 to the union value itself, you would need to do (&bingo.?).bar = 10 which first gets the pointer to the actual union value and assigns to that, instead of to a copy that a lone bingo.? would make.

[Memresable]

So that means If i access one of the fields of the union just to read it, that's a copy on it's own too?
edit: i assume here it just copies the field itself, (which is bar) not the entire union value which is the struct right?

But isn't a union just an integer and a literal union of types in the same memory? can't you access it's memory directly depending on the assignments instead?