From: Rick DeNatale <rick.denatale@...>
Date: 2007-03-02T07:15:31+09:00
Subject: Re: dup and clone

On 3/1/07, Raj Sahae <rajsahae@gmail.com> wrote:
> Why?
>
> irb(main):012:0> a = 5
> => 5
> irb(main):013:0> a.class
> => Fixnum
> irb(main):014:0> a.methods.include?("dup")
> => true
> irb(main):015:0> a.methods.include?("clone")
> => true
> irb(main):016:0> a.dup
> TypeError: can't dup Fixnum
>     from (irb):16:in `dup'
>     from (irb):16
>     from :0
> irb(main):017:0> a.clone
> TypeError: can't clone Fixnum
>     from (irb):17:in `clone'
>     from (irb):17
>     from :0
> irb(main):018:0>
>
>

Because Fixnum's , like some other things like Symbols, nil, true,
false are immediate valued objects, there is only one instance of 1
just like there is only one instance of true, nil, or :abc.  Since dup
and clone are defined to create a new object like the original, they
can't work on these objects.

Now as to why Fixnum has a dup method.  That's just an implementation
choice. It is really getting it from the Kernel module. The
implementation checks the receiver and if it's an immediate object (or
what the implementation code calls a special constant, it throws that
exception.

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/