Re: Multiple iterators for a type

[Jere <jhb.chat@gmail.com>]

On Friday, May 25, 2018 at 11:57:47 PM UTC-4, Luke A. Guest wrote:
> Stephen Leake <> wrote:
> 
> > An "iterator" can be anything you want it to be. As Randy pointed out,
> > there can be only one that gets special treatment from the compiler, but
> > you did not mention that as a requirement.
> > 
> 
> I’m attempting to implement a Unicode string using UTF-8, so I want the
> basic iterator over octets, then the next will iterate over the octets and
> generate code points, then another will be graphème clusters.

When I did multiple iterators I ended up making a package for it, which I 
later adapted just for fun to provide iteration of types in generics.  
The steps I ended up doing were:

1.  Create my Cursor type and Has Element
2.  Create a set of functions returning reference types, but use a package
    to do it so I could pass them into another generic
3.  Instantiate Iterator_Interfaces for my cursor
4.  Implement my iterator
5.  Pass it into a package that created an iterable wrapper

Technically if you just want "in" iteration, you stop at #4, but I like
the "of" version so that is why I made a package for step 5.

In the end I was able to get something like:
for E of Iterable(Container_Object) loop
   E.Do_Things;
end loop;

where Iterable is a function from my generic package that returns
an iterable version of Container object.  It was handy for generics
and having multiple iterators, though it comes at a performance
cost since it uses a layer on top of the container.

Package for making reference types:
https://github.com/jeremiahbreeden/bullfrog/blob/master/src/bullfrog-access_types-references.ads

Package for making "of" iterable wrappers:
https://github.com/jeremiahbreeden/bullfrog/blob/master/src/bullfrog-containers-iterable_wrappers.ads

Package with some predefined wrappers of the standard containers
to my iterable wrappers:
https://github.com/jeremiahbreeden/bullfrog/blob/master/src/bullfrog-containers-predefined_iterable_wrappers.ads

Some testing of the predefined wrappers that I made:
https://github.com/jeremiahbreeden/bullfrog/blob/master/src/tests/test_generic_iteration.adb