return vs. next non-local return in a block

Consider this broken snippet:

def foo
  bar = [1, 2, 3, 4].map do |x|
    return 0 if x.even?
    x
  end
  puts 'baz'
  bar
end
foo # => 0

One might expect return to yield a value for map‘s array of block results. So the return value of foo would be [1, 0, 3, 0]. Instead, return returns a value from the method foo. Notice that baz isn’t printed, which means execution never reached that line.

next with a value does the trick. It acts as a block-level return.

def foo
  bar = [1, 2, 3, 4].map do |x|
    next 0 if x.even?
    x
  end
  puts 'baz'
  bar
end
foo # baz
    # => [1, 0, 3, 0]

In the absence of a return, the value returned by the block is the value of its last expression.