On 10/4/10 6:29 CDT, Steven Schveighoffer wrote:
On Wed, 29 Sep 2010 16:37:34 -0400, Andrei Alexandrescu
<[email protected]> wrote:
On 9/29/10 13:10 PDT, Jacob Carlborg wrote:
Would that be the uniform function call syntax that I've been waiting
for since I first heard of it?
Yah. One unpleasant issue I found with it (as it's already implemented
for arrays) is a chicken-and-egg thing: say I want to provide
operation moveFront only if the type doesn't define it yet. Without
UCF (Uniform Call Syntax) things are simple:
auto moveFront(R)(ref R r)
if (!is(typeof(r.moveFront())) && !hasElaborateCopy!(ElementType!R)) {
return r.front;
}
With UCF things get messy because introducing moveFront at global
level does make r.moveFront() legit, so the if clause returns true,
which is weird because the function shouldn't have been introduced
yet. So the compiler gets confused by this lying Cretan riddle - it
recurses forever (when R is an array).
The solution would be probably to not consider the symbol introduced
until the if-clause has cleared.
__traits(hasMember, r, "moveFront") && rest_of_expression_you_had
-Steve
Yah, I know - in fact I added a trait hasMember(T, "name") to std.traits
that hides the __traits. For some reason that still has issues, probably
due to lack of short-circuit evaluation of && during compilation (but
I'm not positive).
Things are still unpleasant even assuming that works, so I think we need
to look into that when considering committing to uniform call syntax.
Andrei
