Re: [boost] [array] change proposal for the c_array() function

Subject: Re: [boost] [array] change proposal for the c_array() function
From: herve martin (hervemart1_at_[hidden])
Date: 2009-03-15 07:20:36

Niels Dekker wrote:

> No need to change the original implementation of array::c_array()!  Your
>>> change of its return type should be sufficient:
>>>  T (&c_array())[N] { return elems; }
>>>
>>
You are completely right !

>
> Andrey Semashev wrote:
>
>> Why not simply accessing elems directly? It's public.
>>
>
> It looks like it's indeed okay to access boost::array::elems directly. But
> tr1::array::elems is marked as "Exposition only". Other TR1 implementations
> have indeed named their tr1::array data member differently.
>
> Unfortunately c_array() is also specific to Boost.  So I've proposed to add
> this member function to std::array as well (LWG issue #930), returning a
> reference to the array.  (Including overloads for const and rvalue arrays.)
>
>
I argue that c_array() function does not do what we could implicitly expect
from it regarding its name. A C array type encapsulates a pair of
information: its size and its elements type. I guess it's a shame to break
this pair as we usually do.

BTW, a reference on array is implicitly convertible into a pointer on its
1st element. So the change would be really minor. This following lines of
code would still work:
{
array<int,10> toto;
int* item_ptr = toto.c_array();
}

As far as I can see, the only improvement which would be brought by the
change is that sizeof( toto.c_array() ) would return value 10*sizeof(int),
the real size of the C array.

About the array_cast() I will open an other thread.

I'm working also on an array_ref<T,N> class template which exports quite the
same interface as a boost::array and wraps a reference on C array. The main
purpose is to allow an existing C array to be used as a STL sequence
container.

If I can convince about the benefit of these 2 new features, I guess it
would be nice to add them into the existing boost array package as in my
point of view the boost::array class, array_ref class and array_cast
function create a consistent unit.

best regards, herve