As Darren put it in the comments: “DoesItLeak can’t be a struct” We cannot have the DoesItLeak be a struct and safely resolve the strong reference cycle issue.
Value types like structs exist on the stack frame. Closures and classes are reference types.
As the Strong Reference Cycles for Closures section puts it:
This strong reference cycle occurs because closures, like classes, are reference types.
Since the struct has the Variable class and the closure referring to self is stored into the Variable class using subscribeNext, it creates the strong reference cycle. See “Resolving Strong Reference Cycles for Closures” in Automatic Reference Counting Apple documentation.