On Thursday, 4 December 2014 at 09:25:11 UTC, Walter Bright wrote:
http://wiki.dlang.org/DIP69
Despite its length, this is a fairly simple proposal. It adds
the missing semantics for the 'scope' storage class in order to
make it possible to pass a reference to a function without it
being possible for it to escape.
This, among other things, makes a ref counting type practical.
It also makes it more practical to use other storage allocation
schemes than garbage collection.
It does not make scope into a type constructor, nor a general
type-annotation system.
It does not provide an ownership system, though it would
complement one.
So as mentioned, there are various problem with this DIP :
- rvalue are defined as having a scope that goes to the end of
the statement. That mean they can never be assigned to anything
as per spec.
- It add more special casing with & (as if it wasn't enough of a
mess with @property, optional () and the fact the function aren't
first class). For instance *e has infinite lifetime when &(*e) is
lifetime(e).
Also, considering *e has infinite lifetime, (but not e[i] ???)
what is the point of scope at all ? If all indirection goes to
infinite lifetime (ie GC) then lifetime only apply to local
variable and it should not be able to escape these, scope or not.
During discussion, I proposed to differentiate lifetime
calculation between lvalues and rvalues (which are inherently
different beasts with different lifetime) and carry (or not) the
scope flag with each expression.
