The difference between for-loop and each

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

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 19.10.2007 21:19, Andreas S wrote:

procs do

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?

The reason for the behavior you are seeing is different scoping. “for”
does not open a new scope while block parameters sit in a different
scope. Apart from that “for” is a keyword (i.e. part of the language)
while “each” is just a method like other methods.

irb(main):014:0> def f1(x) x.each {|y| p y}; p y end
=> nil
irb(main):015:0> def f2(x) for y in x; p y; end; p y end
=> nil
irb(main):016:0> f1 %w{foo bar baz}
“foo”
“bar”
“baz”
NameError: undefined local variable or method y' for main:Object from (irb):14:inf1’
from (irb):16
from :0
irb(main):017:0> f2 %w{foo bar baz}
“foo”
“bar”
“baz”
“baz”
=> nil
irb(main):018:0>

I’d say it’s a good thing because you get the choice - if you need the
iteration variable after the block then use “for” - otherwise use
“each”.

Kind regards

robert

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