dynamic array memory allocation

[martin]

davidl Wrote:

> It's useful. Seperating the concept of capacity and length should be  
> considered carefully
> 
> > I find myself wondering what actually happens when I create a dynamic  
> > array and concatenate items onto it.  I think I read in a post that  
> > memory will be over-allocated at times to avoid re-allocating.
> >
> > I think it would help out a lot to have an ability to specify  
> > over-allocation.  Something like
> > uint a = [];
> > a.length = 3:10
> >
> > Where the array length is 3, but you are guaranteed to have memory  
> > allocation for 10, so you can be guaranteed that concatenation up to ten  
> > will not need to allocate memory.  This could help in the situation  
> > where there is concatenation in a loop, and the programmer over-sizes  
> > the array before the loop and re-sizes after the loop.
> 
> 
> 
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I can immediately give an example for the usefulness of this from my field:
I'm doing individual-based simulations with many individuals (I'm a theoretical biologist). Typically these individuals reproduce frequently which often involves filling a new array with an unknown number of new objects (if you have discrete generations) or alternatively adding (an unknown number of) objects to an existing array. In C++ being able to do .reserve(large_enough_number) can improve performance considerably.

Martin