Re: [boost] Interest in Boost.Array companion: StaticVector - A statically allocated fixed capacity vector

Subject: Re: [boost] Interest in Boost.Array companion: StaticVector - A statically allocated fixed capacity vector
From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2011-08-14 13:11:04

On Aug 14, 2011, at 2:55 AM, Andrew Hundt wrote:

> I've implemented a small companion class to boost.array that functions like
> a stack allocated vector with fixed capacity. The motivation for this class
> came when I was using boost.array in an interprocess library, when I
> realized that I actually desired an adjustable size boost.array, without the
> complexity of the vector class in the interprocess library. The result is
> StaticVector, which is boost.array directly modified with a size in front of
> the array, and added facilities to match std::vector.
> 
> The Implementation is available at:
> https://github.com/ahundt/Boost.StaticVector
> 
> Sample Code:
>  StaticVector<std::size_t,3> three;
>  three.push_back(5);
>  three.push_back(2);  // size: 2 capacity: 3
>  three.push_back(3);
> 
>  three.push_back(1); // throws std::out_of_range exception indicating the
> capacity has been exceeded
> 
> So here is the big question:
> Is there any interest in the class?

I took a look at the class, and I have a couple of comments:

* Since the underlying storage is "T elems[N]", this means that N different elements get created at construction time. While this is fine for a fixed size array, a variable sized array should start out with no constructions, and create elements as they are added (like vector).

* In operator [] (line 234 and 240), you are asserting if the index is out of range. Again, this may be correct for a fixed size array, but not in a variable sized one. Compare with vector. Also, the assertion is incorrect. Consider the case where N = 10, size = 4, and i = 7.

I like the idea, but I think you need to revisit how the class works.

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists_at_[hidden]>

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