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comp.lang.ruby

freeze and hash

Daniel Schüle

3/12/2006 11:44:00 PM

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
2 Answers

Charles Mills

3/13/2006 12:53:00 AM

0

Schüle 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

Tim Hunter

3/13/2006 12:54:00 AM

0

Schüle 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
>
Freezing the hash doesn't freeze the array that is its default value
(shared with b). See yesterday's thread "Strange behavior" about what's
going on here.

Regarding the deep copy, the usual idiom is Marshal.dump/Marshal.load.