Hi Rob, ----- Original Message ----- From: "Rob Stewart" <stewart@sig.com>
From what I can see, you use the term "program" to mean an instance of class Program or, more specifically, a derivate thereof. That isn't what I think of when I see the word "program."
What would you suggest the name of the class be instead? It is intended to provide the main entry point for a program, so that the program can be easily reused separately.
You cite an example in your article of piping the output of one *nix command to another using the output redirection operator, ">". The correct operator is the pipe, "|". You seem to have codified that misunderstanding, since you've overloaded ">" and not "|" for Program.
Thank you for pointing that out. I don't actually see a need for two different operators for piping and redirection within the library, except that it would be more appropriate for keeping with unix traditions. Ideally I would have one operator "|>" like in Heron.
Finally, your Program class is too intrusive since one must derive from it. It would be better if there was a make_filter() function template called with a function (object) returning a streamable object. Then, make_filter() can return an object which can invoke the function(object) as necessary and can be chained with other instances to create a pipeline.
Why is it considered better to model a concept rather than inherit from a base class and override a virtual function? It seems to me that it is simpler to explain to a newcomer to inherit from a class, and it is more apparent from looking at the code what is actually happening.
(Speaking of "pipeline," that is the *nix term for a series of filters piped together. Hence, your PipeChain class would be better named "Pipeline," and its "ChainTo" member function would be better named "PipeTo.")
Good point.
Oh, I should also point you to Jonathan Turkanis' IOStreams Library (recently accepted, but not yet added to Boost). See http://home.comcast.net/~jturkanis/iostreams/ for code and documentation. Look especially at the filters functionality.
I am sorry but I don't see the connection with the iostreams library and what I am doing. Could you explain the similarities? Thanks for your feedback. CD