What are those pipe symbols for in Ruby?

Toytown_Mafia_21709 0
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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?

syntax ruby
7 Answers

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".

user_260510

The code from the do to the end defines a Ruby block. The word format is a parameter to the block. The block is passed along with the method call, and the called method can yield values to the block.

See any text on Ruby for details, this is a core feature of Ruby that you will see all the time.

unwind_281690 
@names.each do |name|
  puts "Hello #{name}!"
end

at http://www.ruby-lang.org/en/documentation/quickstart/4/ is accompanied by this explanation:

each is a method that accepts a block of code then runs that block of code for every element in a list, and the bit between do and end is just such a block. A block is like an anonymous function or lambda. The variable between pipe characters is the parameter for this block.

What happens here is that for every entry in a list, name is bound to that list element, and then the expression puts "Hello #{name}!" is run with that name.

Philip_Durbin_194640

The equivalent in Java would be something like

// Prior definitions

interface RespondToHandler
{
    public void doFormatting(FormatThingummy format);
}

void respondTo(RespondToHandler)
{
    // ...
}

// Equivalent of your quoted code

respondTo(new RespondToHandler(){
    public void doFormatting(FormatThingummy format)
    {
        format.html();
        format.xml();
    }
});
Jon_Bright_18130

Parameters for a block sit between the | symbols.

dylanfm_387950
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