[Boost-users] [iostreams] Are streams really models of Device?

From: Chad Walters (chad_at_[hidden])
Date: 2007-05-29 21:10:14

Standard stream and stream buffers are supposed to be models of the Device
concept (http://www.boost.org/libs/iostreams/doc/concepts/device.html).

However, I am finding that their treatment by various parts of the library
doesn't seem to be consistent. For example, streams don't actually seem to
be usable everywhere a Device can be used.

For example, if I define SinkOrStream as follows:

using namespace boost::iostreams;

typedef file_sink SinkOrStream;

Then the following declarations compile properly:

SinkOrStream mySink(mFileName);

stream<composite<gzip_compressor, SinkOrStream> > out1(gzip_compressor(),
mySink);

stream<SinkOrStream> out2(mFileName);

However, neither out1 nor out2 compile properly if I define SinkOrStream as:

typedef stream<file_sink> SinkOrStream;

If I understand the documentation correctly, these should both be legal, no?
Does this work for others?

I also find it a little strange that streams are supposed to be models of
Device and they have a close() method, yet they do not support the
closable_tag. Is this by design?

Thanks for any help on clarifying these issues...

Chad Walters