内容简介:Ruby doesn’t have such a feature. It was a shocking discovery when I switched from Java.. a very long time ago.We can somehow trick the language using optional and keyword arguments.
Method Overloading is a programming language feature that allows you to define multiple signatures (and implementations) of the same method.
Ruby doesn’t have such a feature. It was a shocking discovery when I switched from Java.. a very long time ago.
We can somehow trick the language using optional and keyword arguments.
But how can we have real isolated implementations of the same method? I wrote a hack to make this possible based on method arity.
class Foo include MethodOverloading def call puts "foo" end def call(number) puts "foo #{number}" end end foo = Foo.new foo.call # => "foo" foo.call(23) # => "foo 23"
Before I forget, don’t try this in a real-world project . :wink:
Method Definition in Ruby
When Ruby VM evaluates the body of a class, for each method definition, it invokes a special hook that allows you to interact with that method.
class Foo def self.method_added(method_name) super puts method_name end def call end end # => :call
Within that hook, you can have the full reference of the method starting from its name:
class Foo def self.method_added(method_name) super m = instance_method(method_name) puts m.arity end def call(number) end end # => 1
Method Registry
With the combination of method name and arity, you can build a registry of method definitions. These two pieces of information will act as a key, whereas the method itself will be the value.
class Foo @__method_overloading = {} def self.method_added(method_name) super m = instance_method(method_name) method_id = [method_name, m.arity] @__method_overloading[method_id] = m end def foo end def foo(number) end end
Method undef
If you define multiple methods with the same name, Ruby will emit multiple warnings, and it will pick the last method definition.
You can take control of the method dispatching if you undefine the method in the method_added
hook. By doing so, the class won’t reference the method anymore:
class Foo def self.method_added(method_name) super # store in the registry undef_method method_mame end def call end end Foo.new.call # => NoMethodError
Method dispatching
You can use the almighty method_missing
to check the method is in the registry, and execute it:
class Foo def self.respond_to_matching?(method_name, *args) @__method_overloading.key?([method_name, args.count]) end def method_missing(method_name, *args, &blk) super unless self.class.respond_to_matching?(method_name, *args, &blk) self.class.matched_call(self, method_name, *args, &blk) end def respond_to_missing?(method_name, *) self.class.respond_to_method?(method_name) end end
Unbound methods
There is one important detail to know: when a method is undefined, it will become an instance of UnboundMethod
. That means it doesn’t have a context of execution anymore, because it has been removed from the class.
Using #bind_call
and passing the context of execution (the instance of Foo
), Ruby VM will be able to “rebound” the context and correctly execute the method.
class Foo def self.matched_call(instance, method_name, *args, &blk) m = @__method_overloading.fetch([method_name, args.count]) { raise NoMethodError } m.bind_call(instance, *args) end end
Performance
Because of the meta-programming and hand-crafted method dispatching, the code is ~14x slower than regular Ruby code. ♂️
Warming up -------------------------------------- method overloading 24.146k i/100ms method 305.480k i/100ms Calculating ------------------------------------- method overloading 225.254k (±13.5%) i/s - 1.111M in 5.053180s method 3.274M (± 3.5%) i/s - 16.496M in 5.045562s Comparison: method: 3273590.9 i/s method overloading: 225253.9 i/s - 14.53x (± 0.00) slower
Conclusion
Ruby is such a fascinating and flexible language: if you can dream it, you can code it .
很遗憾的说,推酷将在这个月底关闭。人生海海,几度秋凉,感谢那些有你的时光。
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