From: Peter Ertl <pertl@...>
Date: 2006-06-13T23:41:41+09:00
Subject: Re: Getting a list of aliases

I am not sure if I get your question right... maybe this is what you need:

require 'set'

def acts_as_test
  TestClasses.get << self
end

class TestClasses
  @@test_classes = Set.new
  def self.get
    @@test_classes
  end
end

class TestMe
  acts_as_test
end

class TestMeToo
  acts_as_test
end

> TestClasses.get.inspect
#<Set: {TestMeToo, TestMe}>



-------- Original-Nachricht --------
Datum: Tue, 13 Jun 2006 23:19:51 +0900
Von: Daniel Berger <djberg96@gmail.com>
An: ruby-talk@ruby-lang.org
Betreff: Re: Getting a list of aliases

> Ryan Davis wrote:
> > 
> > On Jun 11, 2006, at 7:17 AM, Daniel Berger wrote:
> > 
> >> Is there a way to get a list of instance method aliases somehow?
> >>
> >> # Hypothetical syntax
> >> Array.instance_method_aliases # ['size', 'map', ...]
> >>
> >> If not, I think it would be a nice little bit of extra inspection I 
> >> could use in certain situations, like when I'm in irb and feeling too 
> >> lazy to look at the documentation. ;)
> >>
> >> Actually, this idea struck me when I tried to figure out just the 
> >> "core" methods for a given class and wanted to exclude the aliases.  
> >> At the time, I had to view the source code directly and count them.  
> >> This proved more difficult than I thought, because sometimes methods 
> >> would redefine functions with different names rather than use 
> >> rb_define_alias() in the source code.
> >>
> >> To give you an example of what I mean, in array.c the Array#map 
> >> function is not declared using rb_define_alias(), but is simply mapped 
> >> (no pun intended) to a different function:
> >>
> >> rb_define_method(rb_cArray, "collect", rb_ary_collect, 0);
> >> rb_define_method(rb_cArray, "map", rb_ary_collect, 0);
> > 
> > WARNING: this gets gross:
> > 
> > It is a little less relevant with the core classes (seeing how they 
> > don't change very much), but easier to figure out what is aliased. You 
> > can use ParseTree to get the sexps for the class Array, and then it 
> > becomes pretty "obvious":
> > 
> > ruby -I../RubyInline/dev:lib -rparse_tree -e 'class Array; alias :blah 
> > :map; end; p ParseTree.new.parse_tree(Array)'
> > 
> > [[:class, :Array, :Object, ...
> >   [:defn, :blah, [:fbody, [:cfunc, 504080, 0]]], ...
> >   [:defn, :collect, [:cfunc, 504080, 0]],
> >   [:defn, :collect!, [:cfunc, 504206, 0]], ...
> >   [:defn, :map, [:cfunc, 504080, 0]],
> >   [:defn, :map!, [:cfunc, 504206, 0]], ...
> > ]]
> > 
> > So, with c-implemented functions, your :defn is pretty much just a 
> > pointer to the C-function. You can compare the addresses and see what's 
> > been aliased. Likewise, with a real alias to a :cfunc you can dig a bit 
> > deeper and see that it points to it properly.
> > 
> > In the case of aliases on ruby methods, it gets harder:
> > 
> > % ruby -I../RubyInline/dev:lib -rparse_tree -e 'class X; def y; end; 
> > alias :x :y; end; p ParseTree.new.parse_tree(X)'
> > 
> > [[:class, :X, :Object,
> >   [:defn, :x, [:fbody, [:scope, [:block, [:args], [:nil]]]]],
> >   [:defn, :y,          [:scope, [:block, [:args], [:nil]]]]]]
> > 
> > So, while you can conclude that :fbody is a marker for an alias to 
> > SOMETHING, you can't tell what because it is already expanded. You 
> > should be able to either compare sexps or use some C to dig in and see 
> > that the implementations (nd_body pointer) have the same address. The 
> > code in question is:
> > 
> >>     st_insert(RCLASS(klass)->m_tbl, name,
> >>       (st_data_t)NEW_METHOD(NEW_FBODY(body, def, origin), 
> >> orig->nd_noex));
> > 
> > so the addresses should be the same. (yes, either option is rather
> icky).
> > 
> > 
> 
> Very interesting Ryan, thank you.
> 
> What do you think about adding an Object.aliases method, though?  Or is 
> it just not worth the memory/speed hit?
> 
> Dan