On Sunday, 23 March 2014 at 11:52:53 UTC, Timon Gehr wrote:
On 03/23/2014 01:50 AM, Walter Bright wrote:
2. Can r.front be called n times in a row? I.e. is calling
front()
destructive?
If true, this means that r.front will have to cache a copy in
many cases.
An analogous problem exists and is more severe for
RandomAccessRanges.
import std.algorithm, std.range;
class Obj{ this(int){} }
void main(){
auto x=[1,2,3].map!(a=>new Obj(a));
auto a=x.front;
auto b=x.front;
auto c=x[0];
auto d=x[0];
assert(a is b); // fail
assert(b is c); // fail
assert(c is d); // fail
}
I have an open proposal for a "cache" range adaptor that somewhat
eliviates the problem:
https://github.com/D-Programming-Language/phobos/pull/1364
But it restricts the range to bidirectional (for the reasons
above).
Actually, it's mimited to Bidir, but if you *do* use it as
bidirectional, then 1 element will be evaluated twice. So I'm
wondering if it might not be better to simply restrict it to
forward...
