[C++-sig] Re: Some questions ...

[David Abrahams]

"Mike Thompson" <mike.thompson at day8.com.au> writes:

> "David Abrahams" wrote:
>> "Mike Thompson" writes:
>>
>> > Q2.  The following function works, but I'm left wondering if there's not a
>> >          better way.  It takes a list of ints and returns the equivalent
>> > vector<int>.
>> >
>> >          vector<int>  makeVectorFromList(list l)
>> >          {
>> >              boost::python::object olen = l.attr("__len__")();
>> >              int len = extract<int>(olen)();
>> >
>> >              vector<int> ret(len);
>> >
>> >              for (int i = 0; i < len; ++i) {
>> >                  extract<int>  get_int(l[i]);
>> >                  if (!get_int.check()) {
>> >                      PyErr_SetString(PyExc_TypeError, "makeVectorFromList()
>> > expects a list of ints");
>> >                      throw error_already_set();
>> >                  }
>> >                  ret[i] = get_int();
>> >              }
>> >             return ret;
>> >          }
>>
>> What about that approach would you like to see improved?  In other
>> words, why are you left wondering if there's a "better way"?
>>
>
> I was wondering if I was missing a bit of existing magic like, say, this:
>
>     vector<int> v = extract<vector<int> > (l)();
>
> Except, of course, I tried that and it didn't work.
>
> But I kept wondering if, by writing this function, I was reinventing a wheel
> already built, probably more elegantly.
>
> So I asked.

Well, Ralf has built the wheel that allows the above; see the
Boost.Python FAQ.

I guess I should ask myself why we don't provide that conversion as a
built-in primitive.  It certainly seems doable.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com