I did some research on Ruby on. But... (' ') || ( " ").

I came into a little lesson for Ruby. On this problem i was ask :

Iterators are a way to change our objects. The allow us to execute code on each item in an array or hash. This helps when we want to repeat an action many times on these objects.

Imagine we have a music collection and want to play each song in our collection. We could write an iterator like this:

music  =  ["modern", "classical", "folk"]

music.each  do  |song|
  puts  "play #{song}!"
end

I try this just to see what would happen. I was getting a error

"First output should be hello Edgar".

Notice I'm using Single Quote Marks ( ' ' ) :

names = ['Edgar', 'Gaston', 'Leo', 'Robert']
names.each do |friends|
  puts 'Hello #{friends}!'
end

But when i try it again with Double Quote Marks it runs without a problem.

names = ["Edgar", "Gaston", "Leo", "Robert"]
names.each do |friends|
  puts "Hello #{friends}!"
end

Can anyone explaing to me why this happens? I'm a person the likes to use Single quote marks. I would like to be hear other people opinion.