Question

The python keyword yield has been a great conceptual abstraction for me, allowing me to distill the important parts of an algorithm to human-readable form. We have previously discussed:

Python generators in various languages

where an answer was given for a windows only library in C++. In addition I’ve found another example using a funky macro expansion in the question:

Generators in C++ — invalid use of nonstatic data member

The edge of my computer science knowledge tells me that a yield function has something to do with co-routines and monads, but I’m not quite how this fits into what C++ or C++0x can accomplish.

It seems that in C++, without the using of a macro-expansion or a windows only fiber (thread), yeild can not be implemented. Is this true? Does the question change with the additional language features of C++0x?

Answer 1

You can map yield python mechanism to C++ iterators.

See Boost Function Input Iterator and the example:

The Function Input Iterator allows for creating iterators that encapsulate a nullary function object and a state object which tracks the number of times the iterator has been incremented. A Function Input Iterator models the InputIterator concept and is useful for creating bounded input iterators.

Like the Generator Iterator, the Function Input Iterator takes a function that models the Generator concept (which is basically a nullary or 0-arity function object). Each increment of the function Function Input Iterator invokes the generator function and stores the value in the iterator. When the iterator is dereferenced the stored value is returned.