[pclasses-devel] thoughts about IO layer

[stephan b. <st...@s1...>]

Yo!

Here are some first-draft ideas for the i/o layer. My main goals are:

- Allow interaction between IOStream and IODevice. Either consolidate 
them or provide a marshaller type which can proxy data between them.

- Consolidate the various i/o interfaces (read(), write(), open(),...) 
into a consistent interface.

- Structure the types such that we can apply many generic algorithms to 
them (e.g., std::copy(), std::for_each()).

To be clear: i am not at all certain about any of these ideas. i only 
have experience as a stream user, not a stream implementor.


My first idea is to create an abstract IOInterface type. Something like:

class IOInterface [??? : public NonCopyable] {
	virtual void open() throw(IOError) = 0;
	virtual void close() throw(IOError) = 0;
	virtual size_t read( char * buff, size_t count ) throw(IOError) = 0;
	virtual size_t write( char * buff, size_t count ) throw(IOError) = 0;
	virtual bool canWrite() = 0; // read-only streams return 0
	virtual bool canRead() = 0;// write-only streams return 0
...
};

IOStream should, IMO, subclass std::iostream. i would prefer to see:

class IStream : public IOInterface, public std::istream {}
class OStream : public IOInterface, public std::ostream {}

But this probably requires virtual inheritence to avoid colliding with 
i/ostream members. (haven't checked yet.)

And, of course:

class IODevice : public IOInterface {
....
};

i really would prefer to see IODevice and IOStream be directly related, 
but i am not certain that is really practical or desireable.

Maybe...

istream ==> extended by IDevice ==> IStream

ostream ==> extended by ODevice ==> OStream

IOStream ==> EXTENDS (IStream, OStream)

IODevice ==> EXTENDS (IOStream)

???

In that case, i don't see the real distinction between IODevice and 
IOStream... what IS the difference?

How does all this apply when using IODevice for, e.g., rendering 
graphics (e.g. QPaintDevice). ??? i have no idea.

???


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