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[Bruno Medeiros]

0ffh wrote:
> Bruno Medeiros wrote:
>  > How would the pointer idiom have any advantage in terms of performance??
>  > (versus say, structs with hasNext() and next() member functions)
> 
> Let me take a guess, using arrays and foreach as an example instead of
> general iterables and iteration.
> 
> Foreach with pointers:
> 
>   struct array(T)
>   {
>     T* first;
>     T* after;
>   }
> 
>   void foo(array!(Bar) baz)
>   {
>     // iterate over the members of baz, and doSomethingWith them
>     // the sourcecode
>     //   foreach (elem;baz)
>     //     doSomethingWith(elem);
>     // gets translated to something alike
>     for (Bar* elemPtr=baz.first;elemPtr<baz.after;++elemPtr)
>     {
>       doSomethingWith(*elemPtr);
>     }
>   }
> 
> Using reset(), hasMore() and getNext()
> (I know this is only one of several possibilities)
> 
>   struct array(T)
>   {
>     // internal data structure irrelevant
>     T reset()
>     {
>       // set internal position to first element
>     }
>     bool hasMore()
>     {
>       // check that position is not beyond end
>     }
>     T getNext()
>     {
>       // return current element and increase position
>     }
>   }
> 
>   function foo(array!(Bar) baz)
>   {
>     // iterate over the members of baz, and doSomethingWith them
>     // the sourcecode
>     //   foreach (elem;baz)
>     //     doSomethingWith(elem);
>     // gets translated to something alike
>     baz.reset();
>     while (baz.hasMore())
>     {
>       Bar elem=baz.getNext();
>       doSomethingWith(elem);
>     }
>   }
> 
> 
> Now, where there used to be a few pointer accesses in the other
> version, we have two function calls per iteration.
> In the absolute best case (the array does internally work similar
> to the example above, and functions are inlined) we may get the same
> performance for both. In all other cases the second option is slower.
> 
> Regards, Frank
> 

But indeed the iterator version is trivially inlinable in all it's 
functions, which should make it degenerate in the same code as the array 
pointers version, so that's why I asked why would the pointer idiom be 
more efficient.


-- 
Bruno Medeiros - MSc in CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D