On 03/24/2012 04:07 PM, Stewart Gordon wrote:
On 24/03/2012 18:57, Ali Çehreli wrote:
<snip>
Iterating an output range is also by popFront(). So what it says is,
put this element to
the output range and advance the range. There is a gotcha about this
when the output range
is a slice: Whatever is just put into the range is popped right away!
:) [2]
I'm beginning to get it now: the purpose of an output range is to put
new data into the underlying container. So once you've put something in,
the remaining range is what's left to be populated. I had been thinking
of outputting in terms of appending to the range, hence the confusion.
- Why is a range that can save checkpoints called a "forward" range?
I agree. Here is my guess: The name of the ForwardRange comes from the
fact that it is not
double-ended. It can go only in one direction.
<snip>
Bidirectional ranges are forward ranges as well.
But I've just had a look at STL iterators, and it seems that the range
category hierarchy has been lifted from that. There, a "forward"
iterator combines the functionality of an input iterator and an output
iterator, hence it's your basic iterator that can move forwards and do
what it likes with the data it walks over. (It would seem that it's only
an "output" iterator in that * returns an lvalue, which may or may not
be actually assignable depending on the constancy of the element type.)
In D ranges, OTOH, the only thing that distinguishes a forward range
from a general input range is the presence of a save method to make a
copy of it.
I looked for rationale on Andrei's article. There is this bit about STL
forward iterators:
<quote>
Input and forward iterators are syntactically identical but subtly
different semantically—copying a forward iterator saves iteration state,
but copying an input iterator just creates a new view of the same
iteration state.
</quote>
I guess that's why 'save' is explicit on ForwardRange.
Ali
> Doesn't seem to have anything to do with either the
"forward" name or the C++ origin thereof....
Something else I'm finding puzzling is moveFront, moveAt and moveBack.
Is D trying to be C++11 or something? Move semantics don't seem to me to
be useful in a language with GC.
Stewart.
