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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Performance of element access in Vector
Date: Mon, 19 Jan 2009 20:17:12 -0600
Organization: Jacob Sparre Andersen
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Date: 2009-01-19T20:17:12-06:00
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"Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message 
news:0a8baaf0-19f7-40c0-a041-884e93fa7020@w39g2000prb.googlegroups.com...
...
> A possible conclusion is that for small elements (simple numeric
> types, etc.) it makes sense to access elements by index, when they are
> copied from and into the container. For larger elements the benefit of
> accessing element in-place can be greater than the overhead of
> Update_Element.

Update_Element was added to handle large element types (such as other 
containers) where the overhead of copying them would be prohibitive. I doubt 
that it could be efficient for small objects that can cheaply be passed by 
copy.

> Just to stir the discussion a bit, a straightforward implementation of
> the same test in C++ (with the same base compiler and a single -O2
> option) runs in 13s with indexed access and in 9.5s with iterators -
> both are based on the use of references, which do not exist in Ada.
> Not very easy to neglect this difference.

What happens in C++ when the element whose reference you are using is 
deleted? In Ada.Containers, you'll get Program_Error if you try to do that - 
not a dangling pointer and havoc.

                                  Randy.