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 w

Answer 1

You may want to use instance_exec because it allows you to pass arguments to the block whereas instance_eval does not.

def eval_my_proc_with_args(*args, &block)
  instance_exec(*args, &block)
end

Answer 2

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>

Answer 3

lambda defines a closure which means it will encapsulate the environment it had when it was defined. If you want self to be the caller just define a regular method or better yet use a block.