The Book of Ruby

yield

Let’s see a few more blocks in use. The 4blocks.rb program introduces something new, namely, a way of executing a nameless block when it is passed to a method. This is done using the keyword yield. In the first example, I define this simple method:

4blocks.rb

def aMethod
    yield
end

It doesn’t really have any code of its own. Instead, it expects to receive a block, and the yield keyword causes the block to execute. This is how I pass a block to it:

aMethod{ puts( "Good morning" ) }

Notice that this time the block is not passed as a named argument. It would be an error to try to pass the block between parentheses, like this:

aMethod(  { puts( "Good morning" ) }  )     # This won't work!

Instead, you simply put the block right next to the method to which ...