* lib/forwardable.rb (def_instance_delegator) fix delegating to
'args' and 'block', clashing with local variables in generated
methods. [ruby-core:72579] [Bug #11916]
* lib/forwardable.rb (def_single_delegator): ditto.
If you have a class that uses Forwardable to delegate a method to
another object, and the method that returns the delegate object is
called `args` or `block`, then Forwardable will fail to work.
Here's a simple example:
class ModelCreator
extend Forwardable
attr_reader :args
def_delegator :args, :model_name
def initialize(args)
@args = args
end
end
ModelCreator.new.model_name
If you run the last line above, then you'll get:
NoMethodError: undefined method `model_name' for []:Array
This error occurs because `def_delegator` -- as it is written in Ruby --
uses metaprogramming to add methods to the class that will then delegate
to the delegate object. So it's as if we had written:
class ModelCreator
extend Forwardable
attr_reader :args
def model_name(*args, &block)
args.model_name(*args, &block)
end
def initialize(args)
@args = args
end
end
As you can see, `def_delegator` will not only forward the method call
onto the delegate object, it will also forward any arguments provided as
well. It is here that the bug arises: it splats all of the arguments
into a variable which is called `args`, and because of how variable
scope works in Ruby, it then attempts to call `model_name` on *this*
variable and *not* our delegate object method.
The fix is to call the delegate object method manually using `__send__`.
(This assumes, of course, that the given receiver is, in fact, the name
of a method and not the name of an instance variable, which is also a
possibility.) We use `__send__` because the delegate object method could
be private.
So, that looks like this:
def model_name(*args, &block)
__send__(:args).model_name(*args, &block)
end
Because `def_delegators` and `delegate` use `def_delegator` internally,
they also get this fix as well.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53381 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
986fb55961