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From "Griffin DeJohn (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (LANG-307) CloneUtils - utility class to enable cloning via various different mechanisms
Date Thu, 09 Dec 2010 00:00:05 GMT

    [ https://issues.apache.org/jira/browse/LANG-307?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12967257#action_12967257
] 

Griffin DeJohn edited comment on LANG-307 at 12/8/10 6:58 PM:
--------------------------------------------------------------

Initial version of AutoClone source code attached. Please let me know if you have any comments
or questions, and if anybody can contribute good test cases, I'd appreciate it.

The way it works is this. Given a target object that is a reference type, the first step is
to reflectively create a new instance of the dynamic type of that object. This is accomplished
by trying to invoke each declared constructor in that object's class until a working one is
found (starting with the fewest parameters and working up from there). For each constructor,
an argument to match each parameter is recursively instantiated (with primitives as one base
case, for which the respective default value is passed, arrays as another base case, for which
an empty array of the same component type is passed, and enum types as the last base case,
for which the first declared constant is passed). Once an instance of the target object's
class has been successfully created, all non-static fields in the target object from its class
and superclasses are recursively cloned (with primitives as a base case once again, as well
as Strings and enum types, for which the value is simply assigned to the corresponding field
in the clone), ensuring a deep copy.

It works with the null type, primitive types, reference types, and arbitrarily nested arrays
of any type. Classes that maintain their state partly or wholly in instance variables declared
in a superclass (e.g. StringBuilder) are handled, as are instances of static nested classes,
inner classes (nested in a concrete class or an interface), local classes, and anonymous classes.

It doesn't work yet with an array that contains itself, and it fails with instances of inner
classes (i.e. non-static nested classes) that are dependent on enclosing abstract classes
(haven't figured out a way to dynamically instantiate such a class; any ideas?). It also fails
if necessary fields or constructors are private and can't be made accessible due to a restrictive
security manager, or if a necessary constructor is picky and throws an exception when passed
arguments that don't meet certain requirements, or if a necessary constructor has a parameter
that is an enum type which doesn't declare any constants, or if a necessary constructor has
parameters that can't be instantiated (e.g. abstract classes or interfaces). I'm looking into
using java.lang.reflect.Proxy for that last bit.

The attached version is written to be generic through the use of unchecked casts (the generated
compiler warnings are suppressed). It seems to work well enough, since e.g. "int foo = AutoClone.toClone(0.0d)"
won't compile, but I'd still like to hear what other people think about the type-safety of
my code.

      was (Author: gdejohn):
    Initial version of AutoClone source code attached. Please let me know if you have any
comments or questions, and if anybody can contribute good test cases, I'd appreciate it.

The way it works is this. Given a target object that is a reference type, the first step is
to reflectively create a new instance of the dynamic type of that object. This is accomplished
by trying to invoke each declared constructor in that object's class until a working one is
found (starting with the fewest parameters and working up from there). For each constructor,
an argument to match each parameter is recursively instantiated (with primitives as one base
case, for which the respective default value is passed, arrays as another base case, for which
an empty array of the same component type is passed, and enum types as the last base case,
for which the first declared constant is passed). Once an instance of the target object's
class has been successfully created, all non-static fields in the target object from its class
and superclasses are recursively cloned (with primitives as a base case once again, as well
as Strings and enum types, for which the value is simply assigned to the corresponding field
in the clone), ensuring a deep copy.

It works with the null type, primitive types, reference types, and arbitrarily nested arrays
of any type. Classes that maintain their state partly or wholly in instance variables declared
in a superclass (e.g. StringBuilder) are handled, as are instances of static nested classes,
inner classes (nested in a concrete class or an interface), local classes, and anonymous classes.

It doesn't work yet with an array that contains itself, and it fails with instances of inner
classes (i.e. non-static nested classes) that are dependent on enclosing abstract classes
(haven't figured out a way to dynamically instantiate such a class; any ideas?). It also fails
if necessary fields or constructors are private and can't be made accessible due to a restrictive
security manager, or if a necessary constructor is picky and throws an exception when passed
arguments that don't meet certain requirements, or if a necessary constructor has a parameter
that is an enum type which doesn't declare any constants, or if a necessary constructor has
parameters that can't be instantiated (e.g. abstract classes or interfaces). I'm looking into
using java.lang.reflect.Proxy for that last bit.

The attached version is written to be generic through the use of unchecked casts (the generated
compiler warnings are suppressed). It seems to work well enough, since e.g. "int foo = AutoClone.toClone(0.0d)"
won't compile, but I'd still like to hear what other people think about it.
  
> CloneUtils - utility class to enable cloning via various different mechanisms
> -----------------------------------------------------------------------------
>
>                 Key: LANG-307
>                 URL: https://issues.apache.org/jira/browse/LANG-307
>             Project: Commons Lang
>          Issue Type: New Feature
>          Components: lang.*
>            Reporter: Henri Yandell
>             Fix For: 3.1
>
>         Attachments: AutoClone.java, lang-307.patch
>
>
> Taken from the tasks.html. No idea if we want to do it or not.

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