Re: Dynamically tagged expression required

[Maciej Sobczak <no.spam@no.spam.com>]

Martin Krischik wrote:

>>>Yes. But it only look like the parameter is initialized. Internally the
>>>compiler likely to use a pointer to pass the paramer to speed up things.
> 
>>I don't care. :)
>>I don't want to call something a "pointer" when it isn't in my program.
> 
> I don't care either. But we at c.l.a had to repeat the << "in" is not slower
> then "access" >> mantra so often that we just say it automatily now ;-) .

OK, I see. I think it's "normal" in some way - we (on other forums) are 
busy breaking myths about C++ as well. ;)

As for your mantra - depending on how compiler does its job, "in" might 
be actually *faster* than "access" for the following reason: "access" 
might imply indirection, whereas "in" might be just another (although 
const) name for the actual parameter, especially when the compiler 
inlines the whole call. I don't see anything that would forbid this and 
therefore I wouldn't be surprised to see such "inverse" effects in 
performance measurements. Is this reasoning correct for Ada?

Of course, it is good to follow some coding "wisdom" in order not to 
make things worse or more difficult for the compiler, but AARM 
specifically says that tagged types are passed by reference (6.2). This 
means that passing objects by access variable *only* with hope to get 
better performance would be a premature optimization here (and the root 
of all evil).


-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/