On Tuesday, 2 April 2013 at 15:08:20 UTC, Namespace wrote:
On Saturday, 30 March 2013 at 12:00:32 UTC, Namespace wrote:
As far as I studied the code, something like @ref isn't
possible, because ref is already a keyword. Except as
Pseudo-property. But this is a combination of '@' and 'ref' so
that both, '@ref' and '@ ref' would be valid.
I still like the idea of '&A'.
I have to disagree with me here.
Thanks to this thread
(http://forum.dlang.org/thread/ohjdraaizvwiczifw...@forum.dlang.org)
I know now that after the '@' can be an unlimited number of
white spaces.
Hence my previous speculation that I would have implemented
something wrong is wrong. So is something like '@ref' possible
and already implemented, as you can see here:
https://github.com/Dgame/dmd/tree/rvalue_property
I think this is probably the end result of my little journey.
Any objections?
'@ref' is actually my least favorite choice. Of all presented, my
two favorites are
void func(ref& int a) {}
void func(@val ref int a) {}
Hara Kenji's comment about 'scope ref' also raises the issue of
just how subtle is the difference between this proposed feature
and what 'auto ref' does in templates. Correct me if I'm wrong,
but 'ref&' is proposed to have the compiler create a temporary at
the call site and pass it as a reference.
ref int func1(ref& int a) { return a; }
// Example:
int func2(ref int b) { return a; }
int x = func2(func1(3));
The above passes because the temporary ref to "3" created for
func1 survives the whole expression, I believe. func1 returns the
3 as a ref, which ref should not escape the original expression,
but may escape func1 itself. So 'scope ref' cannot be used.
'scope ref' *could* be used for the related "performance ref"
issue, wherein the compiler decides whether a ref or value is
appropriate knowing full well there's no chance of escaping.
There are actually three ref issues here. The performance ref
issue is related to the compiler making automatic choices which
have no affect on semantics. The other two issues are related to
the Don't Repeat Yourself problem. 'auto ref' is the template
solution which actually creates new functions depending on what
is passed to it. The alternative solution is what's being
proposed here, which I'll call the 'temp ref' solution. Instead
of passing values to a custom created function, all rvalues are
simply converted to temporary lvalues at the call site, with the
caller responsible for tracking the value's scope.
It might seem convenient to use the syntax 'auto ref' to tell a
non-templated function to do this, but that syntax has been
rejected for reasons I either never understood well enough or
I've simply forgotten.
All-in-all, the syntax 'ref &' seems harmless enough to me. As
far as getting it to work with templates, the feature is clearly
mutually exclusive with 'auto ref', but I'm not sure why any
other usage would be a problem.
