[boost] Re: Discovering array size

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2003-12-03 12:15:34

On Dec 3, 2003, at 10:29 AM, AlisdairM wrote:

> Well, I'm trying to use dimension in a non-metaprogramming use-case <g>
>
> We have quite a few places in our codebase where we allow the compiler 
> to
> determine array size for us:
>
> sometype var[] = { initialiser-list };
>
> Often we need to pass this array to some function or library 
> algorithm, and
> then we need the upper bound.  This is not readily available from var
> without resorting to
>
>   sizeof(var) / sizeof(var[0]);
>
> Much nicer to pick it out with
>
>   dimension( var );
>
> So it's not something that can't be worked around, but going directly 
> to
> the answer rather than seeing the calculation and worrying about 
> whether
> packing / alignment is an issue etc. simplifies code reviews etc.
>
> The problem here is obtaining the type of var.  Using a function 
> template
> allows for type-deduction, but does not yield a compile time constant.

I see.  Thanks.  The compile-time version of dimension would be more 
clumsy for you:

dimension<decltype(var)>::value;

Too clumsy?

> Personally, I would rather use tr1::array for this <g> but again we 
> have no
> syntax to deduce array size here so must fall back on traditional C 
> arrays.

<shocking!> :-)

-Howard