Ruby 1.9 Blocks Notes

• Every function can accept a block.


• Kernel.block_given? will tell you if a block was passed.



def test
  a = 42
  yield(a) if block_given?
end



• To assign the block to an argument, you add an ampersand (&) in front of the last argument of your function. This will affect performance.


• You can call the block inside the function using yield or Proc.call like this:



def test(&block)
  a = 42
  yield(a) # or block.call(a,b)
end



• yield calls and passes the arguments to the block.


• block.arity will tell you the number of arguments a block can accept


• If you have a recursive function accepting a block, you can pass the block to it using '&'.



def recursive_function(&block)
  # Do stuff
  recursive_function(&block)
  # pass to other functions accepting blocks
  10.times &block # will run block 10 times
end



• If you use the return keyword inside a block, it will return the value and exit the function binded to the block, which is the one that created it.



def bl(&block)
  yield
end

def test
  bl { return }
  puts "Hello" # this will not be executed.
end



• You can use break to return a value inside a block and stop iterating.



def bl(&block)
  (0..10).each &block 
end

def test
  # This block will stop iterating at 5 and return true.
  bl { |x| (break true) if (x == 5); false }
end