Re: [boost] new version of array<>

From: Mark Rodgers (mark.rodgers_at_[hidden])
Date: 2000-05-27 04:26:50

From: Thomas Holenstein <tholenst_at_[hidden]>
> Furthermore I suggest not making it an aggregate: after
> all, if you want a array of 1000 Elements of a class which
> has no default constructor, you could get quite busy.
> Otherwise it would be possible to have a constructor
> array<..>(const T& elem = T())

I'm not so sure.  As I understand it, the intent was to provide 
a thin wrapper on built-in arrays without the overhead of vector.
If you are going to allow arrays of classes with no default 
constructor, you won't be able to use a built-in array in the 
implementation.  Keep adding "it would be nice to have..." 
features, and before you know it you'll have reinvented vector.

At the other end of the scale, I think one of the principle 
advantages of an array class over vector would be the ability 
to specify an initialisation list.  If it lost this, I doubt I 
would use it; I don't think the overhead of vector is enough 
by itself to make me want something else.

Furthermore, if we want to default initialise all elements in 
arrays of built-in types, can't we just do this:

    array<int,1000> a = {{}};

I don't think that is too bad.  And I don't see anything wrong
with

   array<int,1000> a;
   std::fill(a.begin(), a.end(), 100);

if I want to fill my array with other values.

So in total, I have to say I like the array presented very much
as it is and think it being an aggregate is very important.

Just one minor quibble though.  Shouldn't it be

    void swap (array& y) {
       std::swap_ranges(begin(), end(), y.begin());
     }

and

    template<class T, std::size_t N>
    bool operator== (const array<T,N>& x, const array<T,N>& y) {
        return std::equal(x.begin(), x.end(), y.begin());
    }

and 

    template<class T, std::size_t N>
    bool operator< (const array<T,N>& x, const array<T,N>& y) {
        return std::lexicographical_compare(
            x.begin(), x.end(), y.begin(), y.end());
    }

I'm a bit surprised to see someone who's written a book about the
standard library failing to use it! ;-)

Mark