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

They are different. yield(self) does not change the value of self inside the block, while instance_eval(&block) does.

class Foo
  def with_yield
    yield(self)
  end

  def with_instance_eval(&block)
    instance_eval(&block)
  end
end

f = Foo.new

f.with_yield do |arg|
  p self
  # => main
  p arg
  # => #
end

f.with_instance_eval do |arg|
  p self
  # => #
  p arg
  # => #
end