On Tuesday, 5 March 2013 at 16:12:24 UTC, Steven Schveighoffer
wrote:
On Tue, 05 Mar 2013 03:22:00 -0500, Jonathan M Davis
<jmdavisp...@gmx.com> wrote:
In general, a stream _is_ a range, making a lot of "stream"
stuff basically
irrelevant. What's needed then is a solid, efficient range
interface on top of
I/O (which we're lacking at the moment).
This is not correct. A stream is a good low-level
representation of i/o. A range is a good high-level
abstraction of that i/o.
Ranges aren't necessarily higher- or lower-level than streams;
they're completely orthogonal ways of looking at a data source.
It's completely possible to build a stream interface on top of a
range of characters, which is what I was suggesting. In that
situation, the range is at a lower level of abstraction than the
stream is.
Ranges make terrible streams for two reasons:
1. r.front does not have room for 'read n bytes'. Making it do
that is awkward (e.g. r.nextRead = 20; r.front; // read 20
bytes)
Create a range operation like "r.takeArray(n)". You can optimize
it to take a slice of the buffer when possible.
2. ranges have separate operations for getting data and
progressing data. Streams by their very nature combine the two
in one operation (i.e. read)
Range operations like std.conv.parse implicitly progress their
source ranges. For example:
auto stream = file.byChars;
while(!stream.empty) {
doSomethingWithInt(stream.parse!int);
}
Except for the extra ".byChars", it's just as concise as any
other stream, and it's more flexible than something that *only*
provides a stream interface. It also saves some duplication of
effort; everything can lean on std.conv.parse.
Besides, streams don't necessarily progress the data; C++
iostreams have peek(), after all.
From what I see, at least in terms of the interface, a stream is
basically just a generalization of a range that supports more
than one type as input/output. There's no reason that such a
system couldn't be built on top of a range, especially when the
internal representation is of a single type: characters.
