From: Victor Shepelev <vshepelev@...>
Date: 2006-06-02T05:47:51+09:00
Subject: Re: How use Profiling, a Quick Guide.



From: Dave Howell [mailto:groups@grandfenwick.net]
Sent: Thursday, June 01, 2006 11:36 PM
> >>> * Large number of calls to .size and .length and .count_objects
> >>> methods are a
> >>>   clue some nidjit somewhere is doing something really N^2 stupid
> >>> like...
> >>>    for( i=0; i < container.count_objects(); i++) {
> >>>    }
> >>
> >> question_stack << "What exactly is stupid about that? And what's the
> >> smart alternative?
> > max=container.count_objects()
> > for( i=0; i < max; i++) {
> > }
> >
> > container.each....
> 
> OK, so "container.each" is presumably the smart alternative, and what
> I'd instinctively use anyway, but I don't understand what it is about
> "for( i=0; i < max; i++)" that makes it "really n^2 stupid." 

The point was: if you use some value repeatedly, it is generally smarter to
pre-calculate it.

Example:

def get_some_value
#some long calculation
end

(1..100).each{|i| puts i * get_some_value}

The above code would call get_some_value 100 times. If it rans slowly and
would return 100 same values, the much more smarter way would be

v = get_some_value
(1..100).each{|i| puts i * v}

V.