C# (.NET in general) :)

Well, variables cannot be forced to stack specifically. They are placed in the "local scope". And that would usually be either stack or CPU registers - thinking in stack only is a somewhat flawed mental model.

Both C# and F# complicate this by supporting closures, iterator and async methods which capture variables placing them in a state machine box / display class instead which would be located on the heap, unless stack-allocated by escape analysis (unlikely because these usually cross method boundaries).

However, .NET has `ref structs` (or, in F#, [<Struct; IsByRefLike>] types) which are subject to lifetime analysis and can never be placed on the heap directly or otherwise.