block and yield

yield: 

run what block defines

ex:

def  test(*args, &block)

        yield(*args)

end

test("hello"){ |i| puts i }

---> hello

note:

yield(*args)  = block.call(*args)

when defining a method that receives blocks,

there are two ways

(1)  define method with block arguments

ex:

def test( &block)

end

(2)define method without block arguments

ex:

def test

end

pass arguments to blocks

in the method definition, call yield with arguemtns

ex:

yield (a, b, c)

in the block, use | | to receive arguments 

ex:

| a, b, c|

return value from call block

the return value is last expression evaluated in block

ex:

in the method definition

a= yield