From: Charles Mills <cmills@...>
Date: 2006-03-13T09:53:44+09:00
Subject: Re: freeze and hash

Sch�le Daniel wrote:
> Hello
>
> irb(main):069:0* a = Hash.new([])
> => {}
> irb(main):070:0> a[1] << "X"
> => ["X"]
> irb(main):071:0> a.freeze
> => {}
> irb(main):072:0> a.frozen?
> => true
> irb(main):073:0> b = a.dup
> => {}
> irb(main):074:0> b.frozen?
> => false
> irb(main):075:0> b.default
> => ["X"]
> irb(main):076:0> b[11] << "Y"
> => ["X", "Y"]
> irb(main):077:0> b.default
> => ["X", "Y"]
> irb(main):078:0> a.default
> => ["X", "Y"]
> irb(main):079:0> a.frozen?
> => true
> irb(main):080:0> b.frozen?
>
> as one can see a.default is a flat copy
> so a is modified though it's frozen
>
> what is the usual idom to get deep copy?
>
> Regards, Daniel

Try

a = Hash.new { [] }

When a default value is needed the proc is run and its return value is
used.
See ri Hash.new for more info.

-Charlie