Adding a =~ method to the Method class

Ruby
1

The Ruby API specifies that objects of the Method class have an instance
method “==”: “Two method objects are equal if that are bound to the
same object and contain the same body.”

At this moment, I would very much like it if it also had a “=~” method:
“two method objects are similar if they contain the same body but are
NOT necessarily bound to the same object”

unfortunately I’m not currently skilled enough to really understand the
C code in which the “==” method for the Method class is written. could
someone help me out here? Below I’ve replicated the C code for the “==”
method with some changes to reflect what the =~ method would look like:

static VALUE
method_similar(method, other)
VALUE method, other;
{
struct METHOD *m1, *m2;

if (TYPE(other) != T_DATA || RDATA(other)->dmark !=

(RUBY_DATA_FUNC)bm_mark)
return Qfalse; //I Do Not understand what this if statement does
if (CLASS_OF(method) != CLASS_OF(other))
return Qfalse; //I assume this makes sure that the classes of
both methods is Method?

Data_Get_Struct(method, struct METHOD, m1);//No clue but looks

harmless enough
Data_Get_Struct(other, struct METHOD, m2); //No clue but looks
harmless enough

if (m1->klass != m2->klass ||
    m1->rklass != m2->rklass || //this condition looks like it ALSO

checks that the classes of both methods is Method, so I must be missing
something somewhere…
m1->recv != m2->recv || // <-!! Would all that need to happen is
this line be eliminated??
m1->body != m2->body)
return Qfalse;

return Qtrue;

}

Also, how can you modify Ruby to include this function, so i can use it
in my Rails tests?

-Gabe

2

ruby-1.8.7-p160
add to eval.c, after line 9323:

static VALUE
method_similar(method, other)
VALUE method, other;
{
struct METHOD *m1, *m2;

if (TYPE(other) != T_DATA || RDATA(other)->dmark !=

(RUBY_DATA_FUNC)bm_mark)
return Qfalse;
if (CLASS_OF(method) != CLASS_OF(other))
return Qfalse;

Data_Get_Struct(method, struct METHOD, m1);
Data_Get_Struct(other, struct METHOD, m2);

if (m1->klass != m2->klass || m1->rklass != m2->rklass ||m1->body !=

m2->body)
return Qfalse;

return Qtrue;

}

add to eval.c affter line 10046:

rb_define_method(rb_cMethod, “=~”, method_similar, 1);

3

Hi,

In message “Re: Adding a =~ method to the Method class”
on Thu, 7 May 2009 16:02:09 +0900, Gabriel S.
[email protected] writes:

|At this moment, I would very much like it if it also had a “=~” method:
|“two method objects are similar if they contain the same body but are
|NOT necessarily bound to the same object”

I am not sure how do you use this similarity check? Example?

          matz.
4

On Thu, May 7, 2009 at 9:02 AM, Gabriel S. [email protected]
wrote:

What about

class UnboundMethod
def similar? other
case other
when self.class
self == other
when BoundMethod
self == other.unbind
else
false

or if you prefer

     raise WhateverSeemsFit, "blah"
  end

end
end

class BoundMethod
def similar? other
case other
when self.class
unbind == other.unbind
etc.etc.

Cheers
Robert

–
Si tu veux construire un bateau …
Ne rassemble pas des hommes pour aller chercher du bois, préparer des
outils, répartir les tâches, alléger le travail… mais enseigne aux
gens la nostalgie de l’infini de la mer.

If you want to build a ship, don’t herd people together to collect
wood and don’t assign them tasks and work, but rather teach them to
long for the endless immensity of the sea.

5

Thank you for the quick response!

To answer the other post about an example, The particular use I have for
it was that I had an abstract class deriving from ActiveRecord. It made
sense to override many of ActiveRecord’s class methods: The
AbstractClass methods are passed some params in addition to those
standard to the ActiveRecord method, which it then uses those params to
delegate onto the correct concrete sub class, to which it passes the
standard ActiveRecord params. However, in the subclasses of this
abstract class, I re-instate the ActiveRecord class methods.

So, in order to test that I had actually reinstated the ActiveRecord
methods, I needed to assert that my concrete sub class was using the
ActiveRecord method and not the abstract one.

so…

!(MyAbstractClass.method(:find) == ActiveRecord::Base.method(:find))

but,

MyConcreteSubclass.method(:find) =~ ActiveRecord::Base.method(:find)

incidentally, since posting I attempted to go to bed, but couldn’t, kept
on thinking about the problem, when I remembered vaguely about unbound
methods and came up with this purely ruby method solution:

def test_class_methods_similar(klass1, klass2, method_name_symbol)
unbound_method1 = klass1.method(method_name_symbol).unbind
unbound_method2 = klass2.method(method_name_symbol).unbind
unbound_method1 == unbound_method2
end

The importance of the test truly came out when it helped me catch a bug

  • I had overwritten many methods, and had accidentally overwritten
    destroy with destroy_all.

however, I like the posted solutions better for readability and the fact
that it can be called directly from a class.

and, did that post really come from matz? I ask because seeing as how
I’m fairly new, (to Ruby, to Rails, etc.) and this is my first post ever
to the Ruby forum, I’m feeling a slight sense of awe. just want to say,
Ruby is a beautiful language. It has made me love programming after
many of my college courses had pretty much destroyed any such thought.

I must ask, any chance Method.=~ could make it into the Ruby codebase?
I figure it must have a lot more uses whenever a solution involves
overriding/passing around methods between classes, including most any
use of alias_method?

-Gabe

KDr2 wrote:

ruby-1.8.7-p160
add to eval.c, after line 9323:

static VALUE
method_similar(method, other)
VALUE method, other;
{
struct METHOD *m1, *m2;

if (TYPE(other) != T_DATA || RDATA(other)->dmark !=

(RUBY_DATA_FUNC)bm_mark)
return Qfalse;
if (CLASS_OF(method) != CLASS_OF(other))
return Qfalse;

Data_Get_Struct(method, struct METHOD, m1);
Data_Get_Struct(other, struct METHOD, m2);

if (m1->klass != m2->klass || m1->rklass != m2->rklass ||m1->body !=

m2->body)
return Qfalse;

return Qtrue;

}

add to eval.c affter line 10046:

rb_define_method(rb_cMethod, “=~”, method_similar, 1);

6

Robert D. wrote:

and thanks for this too, now I can add it without having to write C and
recompile!

Cheers
Robert

Cheers indeed!
-Gabe