mirror of
https://github.com/carbon-language/carbon-lang.git
synced 2026-10-01 22:02:45 +01:00
Dana Jansens
3f01310039
This adds support for choice types at a similar level to that of a C enum, where each alternative has a name but no additional data/parameters attached to it. We generate a TODO diagnostic if parameters are specified. Because there's no extra data, the storage is a simple unsigned integer discriminant of the smallest possible size. A choice without any alternatives is not constructible. A choice with a single alternative is, and has an empty tuple in place of a discriminant since it has only one state. The empty tuple is used to make the class non-constructible. This can be improved. Each alternative is turned into a let binding on the choice that is a value of the choice with that alternative set as the active one in the discriminant. This isn't possible to write in user code with a class right now, since the let binding has the same type as the choice (which is a class) it is within. It's possible to generate it in semir however by adding the binding after the class is marked complete.