On Thu, 17 May 2012 11:46:18 -0400, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
On 5/17/12 9:02 AM, Steven Schveighoffer wrote:
Roughly speaking, not all the details are handled, but this makes a
feasible input range that will perform quite nicely for things like
std.algorithm.copy. I haven't checked, but copy should be able to handle
transferring a range of type T[] to an output range with element type T,
if it's not able to, it should be made to work.
We can do this for copy, but if we need to specialize a lot of other
algorithms, maybe we didn't strike the best design.
Right. The thing is, buffered streams are good as plain ranges for one
thing -- forwarding data. There probably aren't many algorithms in
std.algorithm that are applicable. And there is always the put idiom,
Appender.put(buf) should work to accumulate all data into an array, which
can then be used as a normal range.
One thing that worries me, if you did something like
array(bufferedStream), it would accumulate N copies of the buffer
reference, which wouldn't be what you want at all. Of course, you could
apply map to buffer to dup it.
3. An ultimate goal of the i/o streaming package should be to be able to
do this:
auto x = new XmlParser("<rootElement></rootElement>");
or at least
auto x = new XmlParser(buffered("<rootElement></rootElement>"));
So I think arrays need to be able to be treated as a buffering streams.
I
tried really hard to think of some way to make this work with my
existing
system, but I don't think it will without unnecessary baggage, and
losing
interoperability with existing range functions.
I think we can create a generic abstraction buffered() that layers
buffering on top of an input range. If the input range has unbuffered
read capability, buffered() would use those. Otherwise, it would use
loops using empty, front, and popFront.
Right, this is different from my proposed buffer implementation, which
puts a buffer on top of an unbuffered input *stream*. But of course, we
can define it for both, since it will be a compile-time interface.
Where does this leave us?
1. I think we need, as Andrei says, an unbuffered streaming abstraction.
I think I have this down pretty solidly in my current std.io.
Great. What are the primitives?
See here:
https://github.com/schveiguy/phobos/blob/new-io2/std/io.d#L170
Through IODevice. The BufferedStream type is going to be redone as a
range.
3. An implementation of the above definition hooked to the unbuffered
stream abstraction, to be utilized in more specific ranges. But by
itself, can be used as an input range or directly by code.
Hah, I can't believe I wrote about the same thing above (and I swear I
didn't read yours).
Well, not quite :) You wrote about it being supported by an underlying
range, I need to have it supported by an underlying stream. We probably
need both. But yeah, I think we are mostly on the same page here.
4. Specialization ranges for each type of input you want (i.e. byLine,
byChunk, textStream).
What is the purpose? To avoid unnecessary double buffering?
No, a specialization range *uses* a buffer range as its backing. A buffer
range I think is necessarily going to be a reference type (probably a
class). The specialized range won't replace the buffer range, in other
words.
Something like byLine is going to do the work of extracting lines from the
buffer, it will reference the buffer data directly. But it won't
reimplement buffering.
5. Full replacement option of File backend. File will start out with
C-supported calls, but any "promotion" to using a more D-like range type
will result in switching to a D-based stream using the above mechanisms.
Of course, all existing code should compile that does not try to assume
the File always has a valid FILE *.
This will be tricky but probably doable.
Doing this will unify all the i/o packages together into one interface --
File. I think it's a bad story for D if you have 2 ways of doing i/o (or
at least 2 ways of doing the *same thing* with i/o).
-Steve
