Getting Object#inspect back

Ruby
1

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

2

On 10/12/06, OliverMarchand [email protected] wrote:

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

3

Hi –

On Thu, 12 Oct 2006, OliverMarchand wrote:

using .method and .call — I never seemed to link the objects self to
the Object#inspect method

I am sure it is very easy…

super might be adequate:

def inspect
super
end

unless there are multiple overridings along the way, in which case you
might need:

Object.instance_method(:inspect).bind(self).call

David

4

On Thu, Oct 12, 2006 at 11:07:42PM +0900, [email protected] 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.