From: Brian Candler <B.Candler@...>
Date: 2007-04-05T06:12:38+09:00
Subject: Re: Problem Extracting Array Values

On Thu, Apr 05, 2007 at 02:42:04AM +0900, Alex Young wrote:
> Brian Candler wrote:
> >On Thu, Apr 05, 2007 at 01:05:44AM +0900, Dustin Anderson wrote:
> >>is there a simple way in ruby to build an array from a string like this:
> >>
> >>block1,block2,block3 to an array that is like this:
> >>
> >>["block1", "block2", "block3"]
> >
> >I always thought that Object#inspect could be considered as a (crude) form
> >of object serialisation, and it would be really useful to have a reverse
> >"uninspect" operation to recreate the object from it again. Has anyone
> >written such a parser?
> >
> For the basic types, eval will do it to a tolerable degree.

No, that's not what I meant.

Firstly, eval is more dangerous than is wanted. For example, "[3, 4]" can
deserialise as [3, 4], but "3 + 4" should give an error as it would never be
the output of foo.inspect

Secondly, it should also handle regular objects with instance variables. For
example,

irb(main):001:0> class Foo; attr_accessor :a, :b, :c; end
=> nil
irb(main):002:0> obj = Foo.new; obj.a="one"; obj.b="two"; obj.c="three"; obj.inspect
=> "#<Foo:0xb7cd6f70 @c=\"three\", @b=\"two\", @a=\"one\">"

That last string would allow an object of class Foo to be reconstructed
(obviously with a different object_id)

Clearly it won't work for graph-like constructs:

irb(main):001:0> a = nil
=> nil
irb(main):002:0> a = [1, 2]
=> [1, 2]
irb(main):003:0> b = [a, a]
=> [[1, 2], [1, 2]]
irb(main):004:0> a << b
=> [1, 2, [[...], [...]]]
irb(main):005:0> b.inspect
=> "[[1, 2, [...]], [1, 2, [...]]]"
irb(main):006:0>

YAML does all that of course, but it's not inspect.

I just think that using 'inspect' would allow basic objects (with simple
nesting) to be stuffed into a database column in a simple and obvious way,
if there were a safe way to reconstruct them from it.

nil
123
"123\n"
[123, "456"]
{"foo"=>["bar","baz"]}
#<Foo: @var="val">

Regards,

Brian.