On 12/4/10 22:36 CST, Steven Schveighoffer wrote:
On Sat, 04 Dec 2010 11:00:58 -0500, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
On 12/4/10 9:23 AM, Don wrote:
Andrei Alexandrescu wrote:
On 12/4/10 12:42 AM, Don wrote:
Officially, opEquals has to have the signature:
struct Foo {
bool opEquals(const ref Foo x) const {...}
}
This is a compiler bug. For structs there should be no official
implementation of opEquals, opCmp etc. All the compiler needs to worry
about is to syntactically translate a == b to a.opEquals(b) and then
let the usual language rules resolve the call.
Fine, but try to implement a generic type which supports ==.
For example, Tuple in std.typecons.
The only reason that many of the Tuple unit tests pass is that opEquals
never gets instantiated.
I think it should be as follows:
bool opEquals(auto ref inout Tuple rhs) inout {
foreach (i, T; Types) {
if (this[i] != rhs[i]) return false;
}
return true;
}
No no no, inout does not belong here. Use const. inout is only used if
you are returning a portion of the arguments. That should be a hard rule
by the compiler (error).
Fixed:
bool opEquals(auto ref const(Tuple) rhs) const
Then you handle the angry crowds for me please.
How can opEquals be defined in a way that it works for structs with
destructors, and also with rvalues?
"auto ref" should be used whenever you want to accept both a value and
an rvalue. For structs with destructors see my other post in this thread.
Unfortunately, "auto ref" is currently implemented wrongly due to a
misunderstanding between Walter and myself. I meant it as a relaxation
of binding rules, i.e. "I'm fine with either an rvalue or an lvalue".
He thought it's all about generating two template instantiations. In
fact auto ref should work when there's no template in sight.
But it must instantiate two functions, no?
No.
How does one call the same
function with by ref or by value?
By always using ref.
And when inside the function, the code
generation for a ref storage class is going to be drastically different,
right?
No.
BTW, I agree with the point, it should not require templates. But I
think it does result in two functions.
No.
Actually, thinking about it more, how does this work?
T foo();
T bar();
if(foo() == bar())
both are temporaries, but opEquals passes 'this' by reference. So there
we have a case where a reference of a temporary is passed. Does this
make sense?
Yah. Method calls are already passed by reference (I'd prefer not but
that's just me).
Andrei
