[boost] New variant on generator interface

From: Daryle Walker (dwalker07_at_[hidden])
Date: 2002-11-01 01:11:30

Right now, a generator is an object that returns a value from a 
zero-operand operator().  I wonder if we can make a similar concept 
that adds a Boolean conversion to a generator object.  The conversion 
yields TRUE if the object can still return valid items, FALSE 
otherwise.  This is for generators that have a limited usefulness that 
can't be determined in advance.  The standard could have had these kind 
of generators for reading from input streams instead of having a clunky 
iterator adaptor with strange end-iterator properties.  (You can still 
have clunky iterator adaptors, they would define a default-constructed 
iterator with an internal generator that is invalid.)

I'm posting this here because I'm thinking of generator ideas (like 
I/O) that should have this validity check.

Daryle