Re: Performance of element access in Vector

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 21 Jan 2009 05:14:17 -0800 (PST), Maciej Sobczak wrote:

> On 21 Sty, 11:19, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
> 
>>> You mean that arrays have the Iterate method?
>>
>> The language Ada has iteration methods, for example for-loop.
> 
> No, for-loops are not iteration methods, they are control structures.

They are methods of iteration. You mean that for-loop is not a primitive
operation of array. Why should it be?

> Iteration methods are defined by particular interfaces and these are
> different for arrays and Vectors.

Yes, as an ugly hack container libraries provide "foreach" as a primitive
operation. It is even so ugly because neither Ada nor C++ support multiple
dispatch in order to make such a primitive operation truly primitive for
both the container and the element, or maybe for three, including
index/cursor.

>>>> Ordered containers must have array interface.
>>
>>> You mean that containers overload the () indexing? I'm afraid they don't.
>>
>> That containers implement element access using an index from 1D space, if
>> we are talking about iterations.
> 
> This similarity can be interesting as a theory, but is useless in
> practice.

I don't see any problems. For-loops were in practical use long before any
container libraries.

> Can you *reuse* a piece of code that traverses an array (or Vector)
> and apply it to a Vector (or array, respectively)?

You wrap for-loop into a procedure, that is.

> There are two reuse mechanisms in Ada, one with class-wide types and
> run-time polymorphism and one with generics. Neither one can be
> applied to the arrays vs. Vectors problem.

Why? It is trivial to define a primitive operation containing a loop.

> That's why, as far as I'm concerned, arrays and Vectors do not share
> any interface.

They shall share array interface when ordered.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de