r-values can NEVER be accepted by a ref argument, they don't
'exist', we're
talking about implicitly generated temporaries (which also
addresses the
issues with receiving _explicit_ temp's).
They may be temporary but why should that mean they don't exist.
(wow that's disturbingly close to a harry potter quote)
Currently temporaries exist as long as they are required to
exist, and their lifetime never exceeds one statement.
If I were to start arguing upon the basis of your proposal, I
would then
start arguing that auto-ref in this context is pointless, and
automatic
creation of a temp to hold any r-value should be the
universal/default
behaviour.
I believe with the exception of literals (which are probably
implemented as global immutable variables) temporaries are
already whenever an rvalue is used...
Why does the temporary need to exist any longer than the
current
statement? (the current lifetime of temporaries are the
statement or
expression). Surely any longer is just wasting stack space.
scope ref a(scope ref int x) { return x; }
void b(scope ref int x);
b(a(10));
The temp produced from '10' needs to last longer than a(),
because it can
be returned to b(). Ie, the temp needs the life of any normal
local
declared within that scope.
How do you describe 'wasting' stack space? Does D attempt to
recycle stack
space from previous short-lived locals within a single function?
I said "Why does the temporary need to exist any longer than the
current statement?". In your example the temporary does not exist
longer than the current statement, (the current statement in this
example being "b(a(10))" since that is the context in which the
temporary would be created)
I would hope that D reuses the stack space it uses for
temporaries, certainly any decent C++ compiler would...
The important distinction is that with scope ref, a temps life
can be
prolonged and cascaded via return values.
That's simply not true, even if you allow passing rvalues as
normal "ref", as long as DIP25A is implemented. The longest a
temp ever needs to exist is until the end of the statement, with
or without rvalue references. This means there is no issue with
conditionals.
Anyway, it seems in general that everyone thinks DIP25A should be
implemented, or am I mistaken?
