Crosscut

Rust tracks which fields of a struct have moved. Crosscut could do the same for its records, but would that actually be necessary? Having thought about it some more, this whole notion of moving a value out of a field (and moving one back in) only makes sense, if structs are mutable. In Crosscut, records (and any other value) definitely wouldn't be.

So what would that look like, if a language with immutable values had a linear type system? Then moving a field out of a record would create a new value, just like any other modification would. And in this specific case, that new value would have a different type.

Let's say you have a record of type record { a: A, b: B}, and move the value out of the a field. Then the updated record would be of type record { b: B }. You could move another value of type A back in, to replace the original one, and the result would be a record { a: A, b: B } again.