On Wednesday, 3 July 2013 at 16:35:18 UTC, Artur Skawina wrote:
On 07/03/13 18:29, Brad Anderson wrote:
On Wednesday, 3 July 2013 at 11:54:39 UTC, Artur Skawina wrote:
On 07/03/13 02:22, Brad Anderson wrote:
C++11's std::tuple includes a function std::tie that takes
references to the arguments and returns a tuple that
maintains the references to the arguments.
Along with the usual cases where you'd want reference
semantics it also enables this interesting construct for
unpacking tuples.
int a, b;
tie(a, b) = make_tuple(1, 2);
assert(a == 1 && b == 2);
Is there any way to do something similar with
std.typecons.Tuple?
Well, aliases can be used to get a similar effect.
template tie(A...) { alias tie = A; }
tie!(a, b) = tuple(1, 2);
That won't work. a and b aren't held as references (also you
passed them as type parameters :P).
Try it...
And, yes, the fact that 'A...' template parms accept symbols
is not exactly obvious. But it's much more useful that way.
artur
Huh, I had no idea you could do something like that. I stand
corrected. Thanks.
That does get tie = working but doesn't work if you want to pass
it around which is actually more at the heart of what I'm
interested in.
To get straight to the point, I was playing around with
implementing bearophile's enumerate() feature request (something
I've wanted myself). Both his posted solution [1] and my own
quick testing hack (auto enumerate(Range)(Range r) { return
zip(sequence!"n"(), r); }) lose the ability to do ref elements in
foreach that can modify the source range:
---
auto a = ["a", "b", "c"];
foreach(i, ref item; a.enumerate())
item = to!string(i);
assert(a == ["0", "1", "2"]); // fails, a is still ["a", "b", "c"]
---
They don't work because both the tuples he returns from front and
the tuples zip creates aren't references to the originals so you
are just changing the copy stored in the tuple.
Something like "alias RefIntTuple = Tuple!(ref int, ref int);"
gives a compiler error (Error: expression expected, not 'ref').
1. http://d.puremagic.com/issues/show_bug.cgi?id=5550#c2
