asio-users

[asio-users] ..._buffer_container_1

[Alterman, E. <Eugene.Alterman@Staples.com>]

I think it is better to have (mutable_/const_)buffer_conteiner_1 derived
from boost::array<..._buffer, 1>. Then the only thing you need to do is to
add construction from a buffer:

class mutable_buffer_container_1
  : public boost::array<mutable_buffer, 1>
{
public:	
 /// Construct to represent a single modifiable buffer.
  explicit mutable_buffer_container_1(const mutable_buffer& b)
  {
    *begin() = b;
  }
};

Aside from more code, there is another problem with the current approach -
'end()' is defined as 'begin() + 1', but you can use pointer arithmetic
legally only within an array.

Eugene.

Re: [asio-users] ..._buffer_container_1

[Christopher K. <ch...@ko...>]

Hi Eugene,

--- "Alterman, Eugene" <Eugene.Alterman@Staples.com> wrote:

> I think it is better to have (mutable_/const_)buffer_conteiner_1
> derived
> from boost::array<..._buffer, 1>. Then the only thing you need to do
> is to
> add construction from a buffer:
> 
> class mutable_buffer_container_1
>   : public boost::array<mutable_buffer, 1>
> {
> public:	
>  /// Construct to represent a single modifiable buffer.
>   explicit mutable_buffer_container_1(const mutable_buffer& b)
>   {
>     *begin() = b;
>   }
> };

The problem was that I also wanted the return value of asio::buffer()
to be assignable directly into a const_buffer or mutable_buffer, e.g.:

  asio::const_buffer b = asio::buffer(data, size);

or

  asio::mutable_buffer b = asio::buffer(data, size);

Furthermore, in the case of asio::buffer() returning a
mutable_buffer_container_1, I want the "conversion" to mutable_buffer
to be a better conversion than to const_buffer.

Otherwise you get ambiguities with code like:

void foo(const mutable_buffer&);
void foo(const const_buffer&);

char data[1024];
foo(asio::buffer(data));

Using the inheritance here was the only way I could find to make this
the "better" conversion. I'd be happy to know about alternative ways of
doing it.

> Aside from more code, there is another problem with the current
> approach -
> 'end()' is defined as 'begin() + 1', but you can use pointer
> arithmetic
> legally only within an array.

According to the C++ standard, in section 5.7/4 which discusses pointer
arithmetic:

"For the purposes of these operators, a pointer to a nonarray object
behaves the same as a pointer to the first element of an aray of length
one with the type of the object as its element type."

which i took to mean it was legal. I could be wrong though :)

Cheers,
Chris