From: Robert Klemme <shortcutter@...>
Date: 2010-11-09T22:41:27+09:00
Subject: Re: shadow copy and deep copy

2010/11/9 Eva <eva54321@sina.com>:

> x=[1,2,3]
> y=x.dup
>
> this is a shadow copy, I know the theory behind it.

Actually it's called "shallow copy".  And what #dup really does
depends on the class so it could even implement a deep copy (although
that is normally not the case).  In the case of Array you are correct,
it's a shallow copy.

> z=x
>
> is this a deep copy? (z is the deep copy of x?)

No, there is no copy of state at all.  This is called "aliasing": now
both z and x point to the same object.

Example for deep copy:

z = Marshal.load(Marshal.dump(x))

Kind regards

robert

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