Question

I just had a quick question regarding loops in Ruby. Is there a difference between these two ways of iterating through a collection?

# way 1
@collection.each do |item|
  # do whatever
end

# way 2
for item in @collection
  # do whatever
end

Just wondering if these are exactly the same or if maybe there’s a subtle difference (possibly when @collection is nil).

Answer 1

This is the only difference:

each:

irb> [1,2,3].each { |x| }
  => [1, 2, 3]
irb> x
NameError: undefined local variable or method `x' for main:Object
    from (irb):2
    from :0

for:

irb> for x in [1,2,3]; end
  => [1, 2, 3]
irb> x
  => 3

With the for loop, the iterator variable still lives after the block is done. With the each loop, it doesn’t, unless it was already defined as a local variable before the loop started.

Other than that, for is just syntax sugar for the each method.

When @collection is nil both loops throw an exception:

Exception: undefined local variable or method `@collection’ for main:Object