What if method has yield inside, but a block wasn't passed to it?

Question

What happens if you use a method that has a yield, without passing a block to it?

class SomeClass < Array
    def some_method
        yield(self[i])
    end
end

a = SomeClass.new
a.some_method

And is there a way to set a default behavior: give to the method default block to run, if other is not given?

you can check if `block_given?`. `block_given?` will check if block passed to yield. — Pardeep Dhingra, Dec 04 '15 at 19:41
branch on `block_given?`. If it's given, yield to it, else run default behaviour. — Sergio Tulentsev, Dec 04 '15 at 19:41
@Sergio I did that, to be able to use self[i] like in arrays, but messed up my concept. — OlehZiniak, Dec 04 '15 at 19:47
`i` is an undefined local variable. @Sergio's stern admonition about subclassing `Array` applies to most, if not all, of Ruby's built-in classes. The reasons are covered [here](http://words.steveklabnik.com/beware-subclassing-ruby-core-classes). — Cary Swoveland, Dec 04 '15 at 19:59

Simone Carletti · Accepted Answer · 2015-12-04T19:46:07.413

4

You can use Kernel#block_given? to determine if a block is passed and take the appropriate action.

class SomeClass < Array
  def some_method
    if block_given?
      yield(self[i])
    else
      # not given
    end
  end
end

That means you can also have a default action if the block is not passed.

edited Dec 04 '15 at 19:46

answered Dec 04 '15 at 19:42

Simone Carletti

1 Answers1