ruby-core

Issue #9781 has been updated by Benoit Daloze.


Marc-Andre Lafortune wrote:
> I must be tired.
> 
> Nobu: Sorry, I was confused, there's no problem with `UnboundMethod#super_method` because we retain which class this method was accessed from.
> 
> Ryan: That's actually a good example, there is no api to get the "original owner" of an unbound method, so in general it's not possible to implement `super_method` in Ruby. E.g. from `Hash.instance_method(:map)`, I don't know of a way to get back `Hash` in pure Ruby, and thus no way to go through Hash's ancestry chain.

Actually there is a caveat with an UnboundMethod created with Module#instance_method, from a module (and not a class), as it has no idea what is the actual super method (as that can change in different ancestry chains).
Instead it will just return a method if there is a module "M" included in the former module with a corresponding method, and that method might be somewhere in the ancestry of an object including M or not (if "M" was included after).


----------------------------------------
Feature #9781: Feature Proposal: Method#super_method
https://bugs.ruby-lang.org/issues/9781#change-51463

* Author: Richard Schneeman
* Status: Closed
* Priority: Normal
* Assignee: okkez _
----------------------------------------

When `super` is called in a method the Ruby VM knows how to find the next ancestor that has that method and call it. It is difficult to do this manually, so I propose we expose this information in Method#super_location.

Ruby Method class (http://www.ruby-doc.org/core-2.1.1/Method.html) is returned by calling Object.method and passing in a method name (http://www.ruby-doc.org/core-2.1.1/Object.html#method-i-method). This is useful for debugging:

```ruby
# /tmp/code.rb
class Foo
  def bar
  end
end

puts Foo.new.method(:bar).source_location
# => ["/tmp/code.rb", 3]
```

The Object#method allows a ruby developer to easily track the source location of the method and makes debugging very easy. However if the code is being invoked by a call to `super` it is difficult to track down:

```ruby
# /tmp/code.rb

class BigFoo
  def bar
  end
end

class Foo < BigFoo
  def bar
    super
  end
end
```

In this code sample it is easy to find the method definition inside of Foo but it is very difficult in large projects to find what code exactly `super` is calling. This simple example is easy, but it can be hard when there are many ancestors. Currently if I wanted to find this we can inspect ancestors

```ruby
Foo.ancestors[1..-1].map do |ancestor|
  next unless ancestor.method_defined?(:bar)
  ancestor.instance_method(:bar)
end.compact.first.source_location
```

To make this process simpler I am proposing a method on the Method class that would return the result of `super`


It could be called like this:

```ruby
Foo.new.method(:bar).super_method
```

I believe adding Method#super_method, or exposing this same information somewhere else, could greatly help developers to debug large systems easily.




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