Is 'yield self' the same as instance_eval?

Question

Is there any difference if you define Foo with instance_eval: . . .

class Foo
    def initialize(&block)
      instance_eval(&block)         


        

Answer 1

You just can drop the self keyword

class Foo
  def initialize
    yield if block_given?
  end
end

Update from comments

Using yield there is a bit new to my taste, specially when used outside irb.

However there is a big and significant difference between instance_eval approach and yield approach, check this snippet:

class Foo
  def initialize(&block)
    instance_eval(&block) if block_given?
  end
end
x = Foo.new { def foo; 'foo'; end }            
#=> #                                            
x.foo #=> "foo"                                                        
z = Foo.new  #=> #                                            
z.foo #=>NoMethodError: undefined method `foo' for #

Check this one as well:

class Foo2
  def initialize
    yield if block_given?
  end
end
x = Foo2.new { def foo; 'foo'; end } #=> #
x.foo #=> private method `foo' called for # (NoMethodError)
x.send :foo => "foo"
z = Foo.new  #=> # 
z.send :foo => "foo"

As you can see the difference is that the former one is adding a singleton method foo to the object being initialized, while the later is adding a private method to all instances of Object class.