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comp.lang.ruby

getting Object#inspect back

OliverMarchand

10/12/2006 1:43:00 PM

Hello everybody,

Not that I despreately need it, but I was wondering how to e.g. get the
Object#inspect method back for some classes which override it, say just
as an example for a Hash?

Neither option I considered seems suitable:

alias_method --- too late, the original method is gone
instance_eval --- didn't work for me
using .method and .call --- I never seemed to link the objects self to
the Object#inspect method

I am sure it is very easy...
Oliver
3 Answers

Tomasz Wegrzanowski

10/12/2006 2:06:00 PM

0

On 10/12/06, OliverMarchand <oliver.marchand@gmail.com> wrote:
> Hello everybody,
>
> Not that I despreately need it, but I was wondering how to e.g. get the
> Object#inspect method back for some classes which override it, say just
> as an example for a Hash?
>
> Neither option I considered seems suitable:
>
> alias_method --- too late, the original method is gone
> instance_eval --- didn't work for me
> using .method and .call --- I never seemed to link the objects self to
> the Object#inspect method

This is tricky, because Object#inspect calls to_s.
You need to copy both.

class Foo < Hash
define_method(:inspect, Object.instance_method(:inspect))
define_method(:to_s, Object.instance_method(:to_s))
end

a = Foo.new
p a # => #<Foo:0xb7d26d2c>

If you want to keep Hash to_s (but why would anyone want that)
you can do:

class Foo < Hash
define_method(:inspect, Object.instance_method(:to_s))
end

--
Tomasz Wegrzanowski [ http://t-a-w.blo... ]

dblack

10/12/2006 2:08:00 PM

0

Mauricio Fernández

10/12/2006 2:37:00 PM

0

On Thu, Oct 12, 2006 at 11:07:42PM +0900, dblack@wobblini.net wrote:
> >Not that I despreately need it, but I was wondering how to e.g. get the
> >Object#inspect method back for some classes which override it, say just
> >as an example for a Hash?
> >
[...]
>
> super might be adequate:
[...]
> unless there are multiple overridings along the way, in which case you
> might need:
>
> Object.instance_method(:inspect).bind(self).call

It's not enough in this case because there's an explicit check in
rb_obj_inspect that will make it use #to_s if the object is not a "regular
one" (i.e. not Array, Hash, File, etc. nor derived classes):

static VALUE
rb_obj_inspect(VALUE obj)
{
if (TYPE(obj) == T_OBJECT
&& ROBJECT(obj)->iv_tbl
&& ROBJECT(obj)->iv_tbl->num_entries > 0) {
/* .... */
}
return rb_funcall(obj, rb_intern("to_s"), 0, 0);
}

So even if you rebind Object#inspect, it won't do what the OP wanted, but you
can rebind Object#to_s:

a = {}
a.inspect # => "{}"
ins = lambda{|o| Object.instance_method(:to_s).bind(o).call }
ins[a] # => "#<Hash:0xa7dc63cc>"
ins[[]] # => "#<Array:0xa7dc6200>"
ins[Object.new] # => "#<Object:0xa7dc60fc>"

e.g.

class Hash; define_method(:inspect, Object.instance_method(:to_s)) end
{} # => #<Hash:0xa7ddec38>

However, Object#to_s doesn't display instance variables the way Object#inspect
does:

a = {}
ins = lambda{|o| Object.instance_method(:to_s).bind(o).call }
a.instance_variable_set :@a, 1
ins[a] # => "#<Hash:0xa7d93490>"
o = Object.new
o.instance_variable_set :@a, 1
o.inspect # => "#<Object:0xa7d93364 @a=1>"
ins[o] # => "#<Object:0xa7d93364>"


so you'd have to implement another inspect, with recursivity checks and
everything, if you want to imitate Object#inspect.

--
Mauricio Fernandez - http://eige... - singular Ruby