Jonathan Turkanis wrote:
Peter Dimov wrote:
Jonathan Turkanis wrote:
[...]
For example, if I rewrite the following to use read instead of get
template<typename Source> character get(Source& src) { character c = io::get(src); if (c.good() && c == comment_char_) while (c.good() && c != '\n') c = io::get(src); return c; }
Yes, you are right. A "proper" in-place read-based filter that implements the above (minus the bug)
Care to share the bug with me? ;-) I know that the comment character is checked twice, but this seems harmless.
If the first get() returns comment_char_ and a subsequent get() returns EAGAIN before \n is encountered, the next call will return the rest of the comment. You need to remember the "we are in a comment" state. I think.
is much, much harder to write and understand. It will also be much, much faster,
Actually the distinction between an in-place filter and a filter which produces a modified copy of its input is separate from the get/read question. I'm going to provide optimized treament for in-place filters (this is one of the planned changes that's been on hold), but not all filters can be represented that way. It's especially useful for filters which only observe their input, such as line- or character-counting filters, or filters which implement an offset view of the downstream device.
I think that all character-based filters can be represented as in-place read-based filters.
but the character version may be fast enough for most uses.
So all things considered, do you think the basic_character abstraction makes the get() function and the InputFilter concept unreasonably complex?
I'm not sure. -1/io::eof for EOF and -2/io::again for EAGAIN seem good enough to me. I tried to rewrite your comment skipping filter using -1/-2, and it turned out surprisingly complex. I'm no longer sure that the character version is much easier. As with my previous read-based attempt, it exceeded my capability to write code in an e-mail message. ;-) Time for a contest. "Write the best non-blocking comment skipping filter". :-)