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

Subject: Re: [boost] [array] change proposal for the c_array() function
From: Niels Dekker - mail address until 2010-10-10 (niels_address_until_2010-10-10_at_[hidden])
Date: 2009-03-14 10:56:38

herve martin wrote:
> I would submit a simple change request in the boost::array library.
...
> I suggest to change:
> T* c_array() { return elems; }
> 
> into
> T (&c_array())[N] { return *(T(*)[N]) elems; }

Believe it or not, I was considering to submit the very same feature 
request. But go ahead: https://svn.boost.org/trac/boost/newticket 
(Please consider requesting a const overload as well!)

Actually I did the very same request for std::array! But apparently the 
C++ Library Working Group considers a different resolution, adding 
explicit conversion operators instead, converting an std::array to a 
reference to its built-in array: 
http://home.roadrunner.com/~hinnant/issue_review/lwg-active.html#930

BTW, Nicolai Josuttis, the author of boost::array, told me that 
c_array() is only there for historical reasons.

> I have developed a function helper  array_cast<> whose purpose is to:
>  * make a bit more friendly the syntax when casting to a C-array
>  * check consistency between size of the input type and size of the target
> C-array
> 
> for example,
> {
>     long titi;
>     char (&test)[4] = utils::array_cast<char>( titi );
> 
>     test[0] = 0;
> }
> assuming that long is 32 bit long and char is 8 bit long,
> 'test[0]' is now a reference on the  1st byte of 'titi'. Moreover declaring
> test as a char(&)[5] would have failed in compiling since size of both types
> are not suitable (but the function provides some other way to force cast
> when sizes are not compatible)

I'm interested to know if such an array_cast function could be made 
platform independent and safe with respect to byte alignment.

Kind regards, Niels
-- 
Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center