Ruby-块范围

Question

I have a method which I want to act differently depending on the scenario, so I want to be able to pass a block to the method, and execute if the block is given.

However, I am confused by the scope of the variable in the block I am passing in.

For example:

def original_method (a, b, opt = {id: nil, id_map: {}})
  element_id = (opt[:id_map])

  yield if block_given?

end

And the new method which passes the block:

def new_method(a, b, opt)
 original_method (a, b, opt) do
  if(element_id.include? "some text")
    puts "it has some text"
  end
 end
end

But I get the error:

undefined local variable or method `element_id' 

at the yield line.

Can this be done?

Answer 1

You need to pass the local variable element_id , as yield s argument.

def original_method (a, b, opt = {id: nil, id_map: {}})
  element_id = opt[:id_map]
  yield(element_id) if block_given? # pass it as argument
end

Then accept it like :

def new_method(a, b, opt)
 original_method (a, b, opt) do | element_id | # receive as block pramater
  if(element_id.include? "some text")
    puts "it has some text"
  end
 end
end

element_id local variable has been created inside the method original_method , that is why it is accessible inside this method only.

Inside the method new_method , when you are calling the method original_method with a block attached to it, due to closure capability it has access to all variables inside the method new_method from begining to the point where the block is created.

Answer 2

Answer to your indirect question:

Blocks are scoped lexically , meaning that they have access to variables from the scope they're defined in (as opposed to "used in").