syntax - What are those pipe symbols for in Ruby?

Question

What are the pipe symbols for in Ruby?

I'm learning Ruby and RoR, coming from a PHP and Java background, but I keep coming across code like this:

def new 
  @post = Post.new

  respond_to do |format|
    format.html # new.html.erb
    format.xml { render :xml => @post }
  end
end

What is the |format| part doing? What's the equivalent syntax of these pipe symbols in PHP/Java?

Answer 1

They are the variables yielded to the block.

def this_method_takes_a_block
  yield(5)
end

this_method_takes_a_block do |num|
  puts num
end

Which outputs "5". A more arcane example:

def this_silly_method_too(num)
  yield(num + 5)
end

this_silly_method_too(3) do |wtf|
  puts wtf + 1
end

The output is "9".