From: GGarramuno@... (GGarramuno)
Date: 2004-01-22T19:50:02+09:00
Subject: Re: New to Python: my impression v. Perl/Ruby

Dan Doel <djd15@po.cwru.edu> wrote in message 
> We probably shouldn't use #each either, because you can override #each
> to mean anything you want.  Block creation also seems to be less expensive
> than general object creation (or at least range creation), so the 
> performance
> argument is incorrect.
> 

That is indeed interesting!   My idea that for loops were faster were
taken from some ruby online docs stating that as one of the
optimizations to do.  I guess that was true of ruby1.6, perhaps.  Or
the author was just talking about arrays, only.
If I turn the range into an array, the iteration itself is faster,
thou.
It seems for in and by itself is now slow in ruby1.8.1.  And an even
bigger surprise is to find that a while loop performs the slowest
(almost twice as slow now!!!), when it is the one that is not
constructing anything but an integer.  Hmm...
On the positive side, I guess this means there's still quite some room
for optimizing these on a future ruby version.


def do_times(i)
    n = 0
   
    i.times do
        n = n + 1
    end
end

def do_while(i)
  n = 0
  x = 0
   
  while ( x <= i )
    n = n + 1
    x = x + 1
  end
end

def do_each(i)
    n = 0
   
    i.each do
        n = n + 1
    end
end

def do_for2(i)
    n = 0
   
    for k in i
        n = n + 1
    end
end

def do_for(i)
    n = 0
   
    for k in (0..i)
        n = n + 1
    end
end

max = 10000000
t1 = Time.new

do_times max

t2 = Time.new
puts "#times: ", t2 - t1

do_for max

t3 = Time.new
puts "   for: ", t3 - t2

do_while max

t4 = Time.new
puts " while: ", t4 - t3

# Construct these without timing it,
# just to measure loop itself.
# Without turning it into an array, for
# is still slower.  Maybe ruby iterates
# thru ranges internally by turning them into
# arrays first?
r = (0..max).to_a

t5 = Time.new

do_for2 r

t6 = Time.new

puts "  for2: ", t6 - t5

do_each r

t7 = Time.new

puts "  each: ", t7 - t6


######## i got
#times:
6.659
   for:
6.86
 while:
12.097
  for2:
6.55
  each:
7.44


Hmmm... I found the code for ranges in the ruby source and I sort of
understand why this would be so, but I cannot find the for or while
entry functions to trace why this could be.