Re: A few questions

["Randy Brukardt" <randy@rrsoftware.com>]

<briot.emmanuel@gmail.com> wrote in message 
news:aa0cf839-651e-494d-a826-c2ce31a7afd3@googlegroups.com...
>> The "of" form is for iterating over an array or a container whose type 
>> has
>> the Default_Iterator aspect (which gives the iterator to use).
>
> The main drawback, though, is that you then get a Cursor, not an Element, 
> so
> you still need to call the functions Element or Reference to get to the 
> actual
> element. This is slightly less convenient (syntax-wise).

Sure, but not in a case like the OP's, where the "cursor" is the actual data 
and there is no element. In that case, "of" is just overkill.

> I wish it was possible
> to use "of" to indicate that we want to get an element, even when the
> right-side is an iterator (which for instance would be convenient when
> writing graph data structures where there really are lots of different 
> ways
> to iterate, and a single Default_Iterator is not enough

That doesn't make sense, though, as the iterator interface doesn't contain 
the information necessary to do "of" iteration. In particular, it doesn't 
provide the container or Reference function -- nor could it, as there may 
not be a container.

Personally, I find the "of" form unnecessary; we've iterated arrays for 
decades without direct access to the element (using the "cursor", that is 
the array index), so why are containers different? Especially as the 
indexing form works on all of the language-defined containers (you never 
need to explicitly call Reference or Element). So an "in" iterator looks 
just like the array iteration that we've been using from the beginning of 
time. What's so hard about that?

                                        Randy.