How do you know what class defines method foo()?

ruby-talk
1

Hi, folks!

What's the easiest(simplest) code to find a class/module that first
defines a specific method?
I became curious while I was looking for a document of Array#partition
method.
Actually the method is defined in Enumerable module.
But I couldn't guess that it was defined there until I checked Array
class's doc first.
If the inheritance(or mixin) hierarchy is very complex, it will take
long to find a method.

The one I can think of is using MyClass.ancestors and
MyClass.instance_methods recursively (or repeatedly).
Is there a better way?
(On my second thought, singleton classes should also be considered,
right?)

The method prototype might be like...

#returns a class or module which defines the method
def defined_where(obj, method_name)
   ...
end

Thanks.

Sam

2

$ ri partition

--------------------------------------------------- Enumerable#partition
     enum.partition {| obj | block } => [ true_array, false_array ]

···

On 12/22/05, Sam Kong <sam.s.kong@gmail.com> wrote:

Hi, folks!

What's the easiest(simplest) code to find a class/module that first
defines a specific method?

------------------------------------------------------------------------
     Returns two arrays, the first containing the elements of _enum_ for
     which the block evaluates to true, the second containing the rest.

        (1..6).partition {|i| (i&1).zero?} #=> [[2, 4, 6], [1, 3, 5]]

3

Array.method_defined?(:partition)
#=> true

Enumerable.method_defined?(:partition)
#=> true

Same for instance_methods.include?.
If we loop forward through ancestors, we get Array as the answer. If we loop backwards we get Enumerable. The problem is, looping backwards will get us the wrong answer if Array overrides partition. I can't think of a good why to do this unless there is a Class#overrides? method. (e.g. Array.overrides?(:partition) #=> false ).

···

On Dec 22, 2005, at 4:57 PM, Sam Kong wrote:

Hi, folks!

What's the easiest(simplest) code to find a class/module that first
defines a specific method?
I became curious while I was looking for a document of Array#partition
method.
Actually the method is defined in Enumerable module.
But I couldn't guess that it was defined there until I checked Array
class's doc first.
If the inheritance(or mixin) hierarchy is very complex, it will take
long to find a method.

The one I can think of is using MyClass.ancestors and
MyClass.instance_methods recursively (or repeatedly).
Is there a better way?
(On my second thought, singleton classes should also be considered,
right?)

The method prototype might be like...

#returns a class or module which defines the method
def defined_where(obj, method_name)
   ...
end

Thanks.

Sam

4

Array.method_defined?(:partition)
#=> true

Enumerable.method_defined?(:partition)
#=> true

Same for instance_methods.include?.
If we loop forward through ancestors, we get Array as the answer. If we loop backwards we get Enumerable. The problem is, looping backwards will get us the wrong answer if Array overrides partition. I can't think of a good why to do this unless there is a Class#overrides? method. (e.g. Array.overrides?(:partition) #=> false ).

I just played a bit around and found Method#inspect:

a =

=>

a.method(:partition)

=> #<Method: Array(Enumerable)#partition>

a.method(:first)

=> #<Method: Array#first>

a.method(:send)

=> #<Method: Array(Kernel)#send>

class Array; def send *a; super end end

=> nil

a.method(:send)

=> #<Method: Array#send>

So, if just want to know it for one case, use irb and look at Method#inspect.

To write a method that returns the class/module that defines a method one might parse the output of Method#inspect, but I think that is not very nice.

There doesn't seem to be a direct way to get the class/module in Ruby.

Dominik

···

On Fri, 23 Dec 2005 00:12:51 +0100, Logan Capaldo <logancapaldo@gmail.com> wrote:

5

So, if just want to know it for one case, use irb and look at
Method#inspect.

To write a method that returns the class/module that defines a method one
might parse the output of Method#inspect, but I think that is not very
nice.

This is exactly what I wanted.
I didn't know that there's 'method' method.
Thank you very much.

Sam

6

Dominik Bathon wrote:

To write a method that returns the class/module that defines a method one might parse the output of Method#inspect, but I think that is not very nice.

There doesn't seem to be a direct way to get the class/module in Ruby.

But there ought to be. If you think so as well please vote on this RCR:

http://www.rcrchive.net/rcr/show/292

···

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