Re: [Caml-list] Re: generic programming

[John Max Skaller <skaller@ozemail.com.au>]

Francois Pottier wrote:

>On Sat, Jul 06, 2002 at 12:05:30AM +0100, Dave Berry wrote:
>
>>>An iterator is a function that returns a function which maintains a
>>>piece of internal state. 
>>>
>>But can you compile it down to a single increment instruction on a pointer
>>(for an iterator over an array)?
>>

>
>Some ML compilers perform some of these optimizations. O'Caml performs none,
>as far as I know; they are tricky to implement, especially in combination.
>I'd be curious to see how C++ achieves this.
>
Simple: templates use 'textual substitution'. An array iterator IS a 
pointer.
So there is no analysis to do. They're also good at optimising classes
with a single data member (int, pointer, etc).

The one that C++ compilers find hard is to see that the instantiations:

    copy<int*,int*,int*> ...
    copy<unisgned int*,unsigned int*, unsigned int*>

can share the same implementation: programmers usually suppress code bloat
on template instantiation using wrapping tricks, knowing that compilers
aren't yet very smart at it.

-- 
John Max Skaller, mailto:skaller@ozemail.com.au
snail:10/1 Toxteth Rd, Glebe, NSW 2037, Australia.
voice:61-2-9660-0850




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