Resource variables cannot be assigned to, as that would lead to the loss of the variable's current resource value.
Instead, use a swap statement (<->) or shift statement (<- target <-) to replace the resource variable with another resource.
pub resource R {}
var x <- create R()
var y <- create R()
// Invalid: Cannot assign to resource variable `x`,
// as its current resource would be lost
//
x <- y
// Instead, use a swap statement.
//
var replacement <- create R()
x <-> replacement
// `x` is the new resource.
// `replacement` is the old resource.
// Or use the shift statement (`<- target <-`)
// This statement moves the resource out of `x` and into `oldX`,
// and at the same time assigns `x` with the new value on the right-hand side.
let oldX <- x <- create R()
// oldX still needs to be explicitly handled after this statement
destroy oldX
