On Saturday, 23 February 2013 at 20:28:43 UTC, Steven
Schveighoffer wrote:
On Sat, 23 Feb 2013 10:34:18 -0500, deadalnix
<[email protected]> wrote:
On Saturday, 23 February 2013 at 15:16:15 UTC, Steven
Schveighoffer wrote:
This actually is impossible to do with inout, unless your
ranges are pointers or arrays (believe me, I tried with
dcollections). But that is not inout's fault, it's because
we have no way to specify tail-const arbitrary types.
I have read what come after, but clearly shouldn't have. This
is the interesting thing to discuss. Can you expand on that ?
Some code sample ?
OK, here is a simple abstract example (the implementation
details are not important, just the interface).
class Container(T)
{
...
struct range
{
...
@property inout(T) front() inout {...}
void popFront() {...}
bool empty() const { ...}
}
inout(range) opSlice() inout {...}
}
Nice, right? But it doesn't work, for one simple reason:
popFront.
const Container!int cont = new Container!int(...);
auto r = cont[];
foreach(const x; r)
{
writeln(x);
}
doesn't work! typeof(r) is const(Container!(int).range), and
since popFront is not const (and cannot be), you cannot iterate!
What you need is a SEPARATE "const_range" type (this is similar
to C++). Then opSlice() const will return const_range.
And const range and range are not related, they are separate
types. So there is no way to have inout choose the right one!
HOWEVER, if your range is a slice it works beautifully, because
you can do a tail-inout slice inout(T)[].
Not possible with custom types.
I am working on a plan on how to fix this, because it really
annoys me for my project so much to duplicate code that I just
don't even support const ranges or immutable ranges! I do
support immutable and const cursors, since those point at one
element.
But I have not gotten around to pitching it because I need to
come up with a really good solution :) Walter is so sour on
any tail-const solution from past attempts that it has to be
bullet-proof and easy.
-Steve
Steven would you mind to create a topic on this subject precisely
?
