Why are scope variables being deprecated?

[Jonathan M Davis]

On Thursday, October 11, 2012 01:24:40 Piotr Szturmaj wrote:
> Could you give me an example of preventing closure allocation? I think I
> knew one but I don't remember now...

Any time that a delegate parameter is marked as scope, the compiler will skip 
allocating a closure. Otherwise, it has to copy the stack from the caller onto 
the heap to create a closure so that the delegate will continue to work once 
the caller has completed (e.g. if the delegate were saved for a callback and 
then called way later in the program). Otherwise, it would refer to an invalid 
stack and really nasty things would happen when the delegate was called later.

By marking the delegate as scope, you're telling the compiler that it will not 
escape the function that it's being passed to, so the compiler then knows that 
the stack that it refers to will be valid for the duration of that delegate's 
existence, so it knows that a closure is not required, so it doesn't allocate 
it, gaining you efficiency.

- Jonathan M Davis