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comp.lang.ruby

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

Sam Kong

12/22/2005 9:56:00 PM

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
5 Answers

Joe Van Dyk

12/22/2005 11:12:00 PM

0

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?

$ ri partition

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

Logan Capaldo

12/22/2005 11:13:00 PM

0


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
>
>



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 ).

Dominik Bathon

12/23/2005 4:00:00 AM

0

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

> 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

Sam Kong

12/23/2005 6:05:00 AM

0


> 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

Florian Groß

12/23/2005 8:18:00 PM

0