is there a reliable way to find the Object’s Class. I know about
class and type, but what happens if they are overridden?
how do you find it then?
for instance how to find the class at runtime for the following :
class Obj
def class
"Not My Class"
end
def type
"don't look here for it"
end
end
I am sure it is very simple, I just can’t seem to find it.
Any hints would be greatly appreciated.
Thanks,
Walt
···
Walter Szewelanczyk
IS Director
M.W. Sewall & CO. email : walter@mwsewall.com
259 Front St. Phone : (207) 442-7994 x 128
Bath, ME 04530 Fax : (207) 443-6284
is there a reliable way to find the Object’s Class. I know about
class and type, but what happens if they are overridden?
how do you find it then?
for instance how to find the class at runtime for the following :
class Obj
def class
“Not My Class”
end
def type
“don’t look here for it”
end
end
Note that Object#type is on the way out:
$ ruby -ve ‘1.type’
ruby 1.8.0 (2003-06-23) [i686-linux]
-e:1: warning: Object#type is deprecated; use Object#class
As for finding an object’s class without Object#class, I guess you
could do something like:
class Obj; def class; “Go away!”; end; end
=> nil
o = Obj.new
=> #Obj:0x401e98c8
a = ; ObjectSpace.each_object(Class) {|c| a << c if o.is_a?(c)}
=> 346
a[-1]
=> Obj
But ObjectSpace.each_object can also be overridden. There’s a finite
number of ways to get this information, none of which as far as I know
is override-proof.
is there a reliable way to find the Object’s Class. I know about
class and type, but what happens if they are overridden?
You are technically correct that someone /could/ override a class’
class() method, but I think it’s pretty well understood that such a
person would need to be kil^H^H^H discouraged from doing that
So I believe that it is reliable to use the class() method to determine
an object’s class. Have you actually run across a class whose class()
method has been overridden?
As for finding an object’s class without Object#class, I guess you
could do something like:
class Obj; def class; “Go away!”; end; end
=> nil
o = Obj.new
=> #Obj:0x401e98c8
a = ; ObjectSpace.each_object(Class) {|c| a << c if o.is_a?(c)}
=> 346
a[-1]
=> Obj
My problem is in a Persistence Framework that I have, and with
dynamically generated classes from a database schema ( and in a
separate but similar issue with dynamically created classes from a
resultSet).
I need to find the objects class to get the correct database mapping,
but the objects are (in this case) dynamically created from a
database schema, and several of those overide class.
I was hoping to be able to find an objects class from a different
object, perhaps Class. Something like Class.class(obj), that way I
would not have to worry about naming clashes.
The ObjectSpace would work, but I am worried about performance.
Thanks,
Walt
···
Hello --
On Thu, 17 Jul 2003 walter@mwsewall.com wrote:
> Hi,
>
> is there a reliable way to find the Object's Class. I know about
> class and type, but what happens if they are overridden?
>
> how do you find it then?
>
> for instance how to find the class at runtime for the following :
>
> class Obj
> def class
> "Not My Class"
> end
>
> def type
> "don't look here for it"
> end
> end
Note that Object#type is on the way out:
$ ruby -ve '1.type'
ruby 1.8.0 (2003-06-23) [i686-linux]
-e:1: warning: Object#type is deprecated; use Object#class
As for finding an object's class without Object#class, I guess you
could do something like:
>> class Obj; def class; "Go away!"; end; end
=> nil
>> o = Obj.new
=> #<Obj:0x401e98c8>
>> a = ; ObjectSpace.each_object(Class) {|c| a << c if o.is_a?(c)}
=> 346 >> a[-1] => Obj
But ObjectSpace.each_object can also be overridden. There's a finite
number of ways to get this information, none of which as far as I know
is override-proof.
*****************************************************
Walter Szewelanczyk
IS Director
M.W. Sewall & CO. email : walter@mwsewall.com
259 Front St. Phone : (207) 442-7994 x 128
Bath, ME 04530 Fax : (207) 443-6284
*****************************************************
is there a reliable way to find the Object’s Class. I know about
class and type, but what happens if they are overridden?
This is not perfect but working way:
c = Object.instance_method(:class)
class Foo
def class
nil
end
end
f = Foo.new
p f.class # => nil
p c.bind(f).call # => Foo
matz.
Walter Szewelanczyk
IS Director
M.W. Sewall & CO. email : walter@mwsewall.com
259 Front St. Phone : (207) 442-7994 x 128
Bath, ME 04530 Fax : (207) 443-6284
is there a reliable way to find the Object’s Class. I know about
class and type, but what happens if they are overridden?
You are technically correct that someone /could/ override a class’
class() method, but I think it’s pretty well understood that such a
person would need to be kil^H^H^H discouraged from doing that
So I believe that it is reliable to use the class() method to determine
an object’s class. Have you actually run across a class whose class()
method has been overridden?
I tend to agree. Too, this is an instance, if you will, of a larger
question I see with somewhat regularity on this list. Here’s another
instance of the question, see if you can pick out the “class”…
“Is there a reliable way to add numbers? I know about “+”, but what happens
if it’s overridden?”
Sometimes, you just have to trust that people Don’t Do Inordinately Stupid
Things. And have appropriate unit tests.
My problem is in a Persistence Framework that I have, and with
dynamically generated classes from a database schema ( and in a
separate but similar issue with dynamically created classes from a
resultSet).
I need to find the objects class to get the correct database mapping,
but the objects are (in this case) dynamically created from a
database schema, and several of those overide class.
I was hoping to be able to find an objects class from a different
object, perhaps Class. Something like Class.class(obj), that way I
would not have to worry about naming clashes.
How about maybe aliasing the ‘class’ method to something
you can presume nothing could ever clash with?
Silly example:
class Object
alias no_way_in_doodely_heckfire_to_have_name_clash_with_class class
end
