Re: Hash table iterators.

[Lawrence Crowl <crowl at googlers dot com>]

On 11/23/12, Andrew MacLeod <amacleod@redhat.com> wrote:
> On 11/22/2012 01:18 PM, Lawrence Crowl wrote:
> > I have found that tree-flow.h implements iteration over htab_t,
> > while there is no current facility to do that with hash_table.
> > Unfortunately, the specific form does not match the standard C++
> > approach to iterators.  We have several choices.
> >
> > (1) Ignore the problem and leave all such tables as htab_t.
> >
> > (2) Write new hash_table iteration functions to match the form of
> > the existing GCC macro/function approach.
> >
> > (3) Write new hash_table iteration functions to match the form used
> > by the C++ standard.  This approach would entail modifying the loops.
> >
> > Diego and I have a preference for (3).  What do you prefer?
>
> I don't like (1) for sure.
>
> Before deciding a preference between (2) and (3), what are the
> actual differences?  ie, is (2) doing something practical that
> (3) has to bend over for, or is (3)'s format better but wasn't
> practical before?  is (2) otherwise useful going forward?

For iterating over a hash table containing elements of type T,

(2) The for statement is parameterized by an iterator variable and a
variable of type T.  The loop copies the element into the T variable,
and that variable is used in the body.

(3) The for statement is parameterized only by an iterator variable.
The loop uses "*iterator_variable" to obtain a reference to the
element.

With (3), we have well-established practice for writing generic
algorithms.  With (2), we seem to have just for loops.

-- 
Lawrence Crowl