Say we have a class that we cannot change,
class C
def foo
super
puts "Low!"
end
end
We'll need to dynamically define the method foo
in something that we'll be able to inject into C's ancestry chain. The behavior of super
must be specific to a given object, not class-wide. We'll be able to enclose that logic into an anonymous module (let's name it for now):
module M
def foo
puts "High!"
end
end
Extending an instance of C
with the module:
c = C.new
c.extend(M)
c.foo
# High!
will not work since we've put the method from the module before the method we've defined in the class. Looking at our object's ancestors
c.singleton_class.ancestors
# => [#<Class:#<C:0x00005652be630b20>>, M, C, ...]
I came up with an ugly workaround, which is redefining the methods from our class in our singleton_class, ie
c.define_singleton_method(:foo, c.class.instance_method(:foo))
c.foo
# High!
# Low!
While this works (does it work? I've tested it for a bit and it seems to, but I'm no longer certain), I wonder whether I'm missing something obvious and there's an easier way to dynamically define a "super" method for an instance of a class.
To be clear, we want to be able to extend another instance of C
with another module, ie
C.new.extend(Module.new do
def foo
puts "Medium!"
end
end).foo
# Medium!
# Low!
and have its output not tainted by other instances.
Now that I understand you're trying to work around an issue in some third-party code, I can suggest a more reasonable solution. In the code below, I'm thinking that B
and C
are defined by the gem and you don't want to change their source code, but you want to inject some code into the place where C#foo
calls B#foo
.
class B
def foo
puts "Highest!"
end
end
class C < B
def foo
super
puts "Low!"
end
end
module CE
def foo
super
foo_injected
end
end
C.include(CE)
module M
def foo_injected
puts "High!"
end
end
c = C.new
c.extend(M)
p c.singleton_class.ancestors
c.foo
The output is:
[#<Class:#<C:0x000055ce443366a8>>, M, C, CE, B, Object, Kernel, BasicObject]
Highest!
High!
Low!
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