The difference between for-loop and each

Hopefully (I’m sure) somebody can shed a light on this. This caught me
by surprise

ruby 1.8.6 (2007-03-13 patchlevel 0) [i686-linux]
test.rb:
TEST = []
def procs &block
TEST << block
end

#for n in [1,2,3] do
[1,2,3].each do |n|
procs do
puts “#{n}”
end
end

TEST.each do |t|
puts t
t.call
end

With for loop

ruby test.rb

3

3

3

With each

ruby test.rb

1

2

3

I thought for-loop behaves the same as each. Apparently not. Why is this
and is this a good thing?

Thank you in advance
-andre

On 10/19/07, Andreas S [email protected] wrote:

end
t.call

and is this a good thing?

Thank you in advance
-andre

They are not quite the same. for does not introduce a new scope, whereas
each does. So, each time through the for loop, the closures you are
stashing
in TEST are all referencing the same scope. When you run the stashed
procs,
you are in that same scope, n has the value 3 at the end the for
statement
so that is what is printed.

In the each version, you get a new scope and hence a new n each time
through
the loop, so the value of n saved in each closure is different.

Try the following:

for n in [1, 2, 3] do puts n end
puts n
[1, 2, 3].each do |m| puts m end
puts m

As for rationale - for is slightly faster (no new scope has to be
created
each time round the loop) and is similar in appearance to for statements
in
other languages. However, the scope issue breaks it in my opinion and I
never use it.

Regards,
Sean

This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.

| Privacy Policy | Terms of Service | Remote Ruby Jobs