Bug #19079
closedModules included in a DelegateClass cannot override delegate methods
Description
Because DelegateClass
defines delegate methods on the class itself, those delegate methods come first in the method lookup chain. This prevents included modules from overriding delegate methods:
Base = Class.new do
def foo
"base"
end
end
Helper = Module.new do
def foo
"helper"
end
end
WithHelper = DelegateClass(Base) { include Helper }
WithHelper.new(Base.new).foo
# => "base"
One possible solution would be to define the delegate methods in a separate module. That way, other modules could come before it in the method lookup chain.
Updated by jonathanhefner (Jonathan Hefner) about 2 years ago
I have submitted a PR with the proposed solution: https://github.com/ruby/delegate/pull/14.
Updated by matz (Yukihiro Matsumoto) almost 2 years ago
- Status changed from Open to Rejected
The DelegateClass
defines an anonymous class and defines forwarding methods to the class. The reported (so-called) issue is a natural consequence of the above behavior. include
add methods defined in a module above the current class, so forwarding methods have higher precedence. If you (re)define a method, it overwrites the forwarding method.
My opinion is that your assumption is wrong, so we don't need to fix. If you think we need to implement your assumption, you need to persuade us with the real world use-case.
Matz.
Updated by matz (Yukihiro Matsumoto) almost 2 years ago
- Related to Bug #19047: DelegateClass displays "method redefined" warning when overriding methods added
Updated by matz (Yukihiro Matsumoto) almost 2 years ago
If you want to include a module to a delegated class, try the following:
class WithHelper<DelegateClass(Base)
include Helper
end
Matz.
Updated by Hanmac (Hans Mackowiak) almost 2 years ago
you can also try prepend instead of include:
WithHelper = DelegateClass(Base) { prepend Helper }
Updated by jonathanhefner (Jonathan Hefner) almost 2 years ago
This issue occurred for a private module in Rails: https://github.com/rails/rails/pull/46189#discussion_r991440668.
Using include
in a subclass works. Using prepend
also works, and is the workaround I used for the Rails module.
However, my proposed solution for this issue (https://github.com/ruby/delegate/pull/14) also solves #19079 with a performance improvement.
I opened this issue and #19079 because the current behavior seemed surprising to me. In particular, I expected the DelegateClass
block to behave just like a Class.new
block. I feel like that is a reasonable assumption based on the documentation.
But, if my assumption is wrong, then I understand the decision.