Provide value for self when using Proc#call

Question

When using Proc#call to call a lambda function in Ruby, self always ends up with the value that it had when the function was defined, rather than the value it has when the function is called, for example:

$p = lambda { self }  class Dummy   def test     $p.call   end end  d = Dummy.new  > d.test => main 

Calling test returns main, when what I intended it to return is #<Dummy:0xf794> - an instance of Dummy, which was the value of self at the point in the code where I called $p.

In Javascript, I would just pass the object that I want to be the "callee" as the first argument to call. Is there any such functionality in Ruby, allowing me to set an arbitrary object, or at least the current value of self, as the new value for self when I call a Proc?

Answer 1

You're looking for instance_eval, which evaluates a lambda in the context of the calling object.

>> $p = proc { self } => #<Proc:0x95cece4@(irb):1 (lambda)> >> class Dummy >>   def test >>     $p.call >>   end >>  >>   def test1 >>     instance_eval(&$p) >>   end >> end  >> d = Dummy.new => #<Dummy:0x946f7c8> >> d.test => main >> d.test1 => #<Dummy:0x946f7c8>