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Matthew Jaggard  
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 More options Apr 23 2012, 7:57 am
From: Matthew Jaggard <matt...@jaggard.org.uk>
Date: Mon, 23 Apr 2012 12:57:08 +0100
Local: Mon, Apr 23 2012 7:57 am
Subject: Cloning constructor
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I'm not sure how common a design pattern this is, but I've just had to
implement a cloning constructor (see below) could Lombok create this for me?

@Data
public class Blah
{
   private int field1;
   private int field2;
   private int field3;

   public Blah(Blah toCopy)
   {
      this.field1 = toCopy.field1;
      this.field2 = toCopy.field2;
      this.field3 = toCopy.field3;
   }


 
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Reinier Zwitserloot  
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 More options Apr 23 2012, 5:50 pm
From: Reinier Zwitserloot <reini...@gmail.com>
Date: Mon, 23 Apr 2012 14:50:27 -0700 (PDT)
Local: Mon, Apr 23 2012 5:50 pm
Subject: Re: Cloning constructor
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We could make an annotation that would make one for you, certainly. Lombok
does not currently ship with such an annotation + handler, though.


 
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Matthew Jaggard  
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 More options Apr 23 2012, 6:38 pm
From: Matthew Jaggard <matt...@jaggard.org.uk>
Date: Mon, 23 Apr 2012 23:38:23 +0100
Local: Mon, Apr 23 2012 6:38 pm
Subject: Re: [project lombok] Re: Cloning constructor
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Thanks Reiner.
I guess my reservation is that this is the first time I've wanted one in my
current project, and I don't remember wanting loads before. It just seemed
like a lots of typing for a fairly simple concept. Have other people come
across this? It's not worth putting in if it's not at all common.

I guess @CloningConstructor would be a reasonable name? I would also assume
that it would only make shallow copies of things, but that would have to be
documented (so that if you have a Collection in your object, you don't
expect the contents of the new one to remain static when you update the
original).

On 23 April 2012 22:50, Reinier Zwitserloot <reini...@gmail.com> wrote:


 
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Kevin Ludwig  
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 More options Apr 23 2012, 6:54 pm
From: Kevin Ludwig <kevin.lud...@gmail.com>
Date: Mon, 23 Apr 2012 15:54:48 -0700
Local: Mon, Apr 23 2012 6:54 pm
Subject: Re: [project lombok] Re: Cloning constructor
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maybe I'm missing something but can't you just implement cloneable? Doesn't
that automatically provide a clone() method that does shallow copies?

On Mon, Apr 23, 2012 at 3:38 PM, Matthew Jaggard <matt...@jaggard.org.uk>wrote:

--
Kevin

 
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Tumi  
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 More options Apr 24 2012, 6:37 am
From: Tumi <elbailedelmil...@gmail.com>
Date: Tue, 24 Apr 2012 03:37:02 -0700 (PDT)
Local: Tues, Apr 24 2012 6:37 am
Subject: Re: Cloning constructor
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Yes, but the native Object.clone implementation can be 800% or 1000%
slower than this way...
Regards

On Apr 24, 12:54 am, Kevin Ludwig <kevin.lud...@gmail.com> wrote:


 
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Matthew Jaggard  
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 More options Apr 24 2012, 7:14 am
From: Matthew Jaggard <matt...@jaggard.org.uk>
Date: Tue, 24 Apr 2012 12:14:28 +0100
Local: Tues, Apr 24 2012 7:14 am
Subject: Re: [project lombok] Re: Cloning constructor
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This page lists quite a lot of problems with clone()

http://en.wikipedia.org/wiki/Clone_(Java_method)

On 24 April 2012 11:37, Tumi <elbailedelmil...@gmail.com> wrote:


 
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Reinier Zwitserloot  
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 More options Apr 24 2012, 7:31 am
From: Reinier Zwitserloot <rein...@zwitserloot.com>
Date: Tue, 24 Apr 2012 12:31:03 +0100
Local: Tues, Apr 24 2012 7:31 am
Subject: Re: [project lombok] Re: Cloning constructor
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Yeah, the 'is this actually common boilerplate' issue stuck us too. Also,
usually a copy constructor does a little more than 'just' copy fields, so
how do we let you add some code? That's harder than it looks, at least if
we want to do it in a way that makes it easy to understand and does not
require you to dig through a lot of documentation to figure out how it
works (i.e. no 'magic methods' which are called at the end).

 --Reinier Zwitserloot

On Tue, Apr 24, 2012 at 12:14, Matthew Jaggard <matt...@jaggard.org.uk>wrote:


 
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Matthew Jaggard  
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 More options Apr 24 2012, 8:06 am
From: Matthew Jaggard <matt...@jaggard.org.uk>
Date: Tue, 24 Apr 2012 13:06:32 +0100
Local: Tues, Apr 24 2012 8:06 am
Subject: Re: [project lombok] Re: Cloning constructor
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In my particular case, I don't actually want to do any more than copy the
fields. If you did, could you have a parameter to the annotation like this?

@Data
@CopyConstructor(after="postCopy")
public class MyObject
{
   private int field1;

   private void postCopy()
   {
      field1 = 23;
   }

}

Obviously this creates nasty issues like what to do if the method doesn't
exist? (Error at compile time)
The other option I see (again, I'm not sure if this is possible?) is to
have a separate annotation like @AfterCopyConstructor

@Data
@CopyConstructor
public class MyObject
{
   private int field1;

   @AfterCopyConstructor
   private void postCopy()
   {
      field1 = 23;
   }

}

In this case, what happens if @AfterCopyConstructor is defined on a method
but @CopyConstructor is not defined? (Fail to create the constructor
silently?)

On 24 April 2012 12:31, Reinier Zwitserloot <rein...@zwitserloot.com> wrote:


 
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Roel Spilker  
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 More options Apr 25 2012, 5:26 am
From: Roel Spilker <r.spil...@topdesk.com>
Date: Wed, 25 Apr 2012 11:26:28 +0200
Local: Wed, Apr 25 2012 5:26 am
Subject: Re: [project lombok] Re: Cloning constructor
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I like to use final fields a lot, so I having a postCopy method is no
solution is I would like to clone/modify the contents of the fields in
the constructor.

On 24-4-2012 14:06, Matthew Jaggard wrote:


 
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Matthew Jaggard  
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 More options Apr 25 2012, 5:44 am
From: Matthew Jaggard <matt...@jaggard.org.uk>
Date: Wed, 25 Apr 2012 10:44:56 +0100
Local: Wed, Apr 25 2012 5:44 am
Subject: Re: [project lombok] Re: Cloning constructor
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Hmm. I'm guessing the IDE / javac wouldn't be clever enough to work out
that the following is technically OK...

public class MyClass
{
  private final int i;

  public MyClass(MyClass copyOf)
  {
    afterCopy();
  }

  private void afterCopy()
  {
    i = 23;
  }

  //afterCopy is never called in the rest of the class.

}

Although actually, this is kind of irrelevant because the constructor has
to NOT initialise the final variable "i" - and we have no way of knowing
that's the case, unless you had YET ANOTHER annotation called
@CopyNonFinalConstructor or something?!

It's getting too complicated. Maybe it's just not worth adding at all?

On 25 April 2012 10:26, Roel Spilker <r.spil...@topdesk.com> wrote:


 
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Maaartin G  
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 More options Apr 25 2012, 7:32 am
From: Maaartin G <grajc...@seznam.cz>
Date: Wed, 25 Apr 2012 04:32:28 -0700 (PDT)
Local: Wed, Apr 25 2012 7:32 am
Subject: Re: [project lombok] Re: Cloning constructor
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On Wednesday, April 25, 2012 11:26:28 AM UTC+2, Roel Spilker wrote:
> I like to use final fields a lot, so I having a postCopy method is no

solution is I would like to clone/modify the contents of the fields in the
constructor.

Exactly. This is my major problem both with the proposed CloningConstructor
and the clone() method. My second largest problem is the need to "unshare"
some members via something like list = new ArrayList(original.list). I
intentionally don't write "deep copy", since it goes just one level deep
(in fact I don't think I ever needed a real deep copy).

What I needed is something like

@lombok.RequiredArgsConstructor
class Something {

    private final Date date;
    private final int x, y, z;
    private final List list;

    @lombok.Complete
    public Something(Something original) {
        // here Lombok inserts missing assignments for x, y, and z
        list = new ArrayList(original.list);
        date = new Date(original.date.getTime());
    }

}

This could be brought a bit further like

    @lombok.Complete
    public Something(Something original, int x) {
        // here Lombok inserts missing assignments for x, y, and z
        this.x = x;
        list = new ArrayList(original.list);
        date = new Date(original.date.getTime());
    }


 
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Karsten Tinnefeld  
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 More options Apr 25 2012, 5:52 pm
From: Karsten Tinnefeld <k.tinnef...@googlemail.com>
Date: Wed, 25 Apr 2012 14:52:31 -0700 (PDT)
Local: Wed, Apr 25 2012 5:52 pm
Subject: Re: [project lombok] Re: Cloning constructor
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In a anemic data object generator before our time, we had copy() methods
which generated copy() methods on the source objects to produce a new
object. That way, you could access private target fields with

   1. assignments on simple values: newObject.a = a;
   2. produce copies on complex values: newObject.b = b.copy();
   3. optionally create deep copies on arrays: newObject.c = new
   XXX[c.length]; System.arraycopy(c, 0, d, 0, c.length);
   4. optionally create deep copies on collections: newObject.d.addAll(d);
   // where newObject.d was initialized as some Collection in the constructor.
   5. newObject = (XXX) this.clone() if everything else failed.

We missed out the special java.util.Date case. Date should be considered
immutable by convention.
I guess that lombok could not distinguish between cases 1 or 2 and the
option in 3/4 would need a switch as well.


 
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Peter Grant  
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 More options Oct 4 2012, 4:04 pm
From: Peter Grant <peter.c.gr...@gmail.com>
Date: Thu, 4 Oct 2012 13:04:47 -0700 (PDT)
Local: Thurs, Oct 4 2012 4:04 pm
Subject: Re: [project lombok] Re: Cloning constructor
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Is anyone still interested in lombok annotations for this?  I've written a
javac handler that does some of the things described here and would be
happy to contribute that and more.  However most of my use cases center
around interfaces, so I'm primarily interested in generating conversion
constructors that assign fields based on calling getters in an implemented
interface or superclass.

I still have plenty of work to do, but I have implemented the following so
far:

1. Copying a basic data contract.  If two classes implement the same
interface and have fields defined such that an @Data annotation generates
implementations of the interface, annotating the classes with
@CopyConstructor(TheSharedInterface.class) will generate a conversion
constructor with an argument of TheSharedInterface.  Some customization
would be useful here.
2. Deep copying of any class whose members all have a deep copy
constructor.  Whether to try deep or shallow copying is a configuration
option.  The trouble with deep copying is of course all of the iterables.
3. Deciding when to call super and throwing errors if we can't handle
anything super likely didn't handle for us.
4. Determining type parameters for generics (including for deep copying and
when inheritance and generics are involved).

The parts I have not yet implemented (but plan to) include:

5. Handle iterables. If the result of a getter is an iterable, the field
type might hint at which iterable to use (i.e. List<T> field1 or
LinkedList<T> field2).  If no implementation class is specified, I will
probably end up picking a default per collection type.
6. Enable constructor extensibility.  I have currently defined an
@CopyConstructor annotation at the class level, with an optional class
argument telling it what type to copy from.  I like the idea of having a
class-level annotation, since requiring a constructor would mean requiring
unnecessary boilerplate.  Perhaps I could change the annotation to be
definable at the class or constructor level: if it's at the class level,
generate the constructor; if it's on a constructor, inject the generated
code into the start of the constructor.

I've toyed with generating multiple constructors, compositing constructors,
and static factory methods, but I didn't like where I got with any of that.
(Example: constructors on a class are obvious, but how do you know a static
method is a factory method if it's already been compiled and your
annotation has a source retention policy?  That makes it nigh impossible to
do deep copying.)

If there is any interest in including something like this in lombok, I
would be happy to share it and keep plugging away on it.  Of course the
biggest thing missing, by far, is the entire Eclipse implementation, but
there are some other features that might be desirable to a broader
audience, such as support for fluent getters or direct field access.  

Anyway, it's a start.  Thoughts?


 
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Reinier Zwitserloot  
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 More options Oct 6 2012, 1:44 pm
From: Reinier Zwitserloot <reini...@gmail.com>
Date: Sat, 6 Oct 2012 10:44:13 -0700 (PDT)
Local: Sat, Oct 6 2012 1:44 pm
Subject: Re: [project lombok] Re: Cloning constructor
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I think its cool but I worry that it becomes a feature that sees very
little use and becomes a pain to maintain. There is so much that can be
configured about this sort of thing, so do we make it as simple as possible
and simply resort to: "Well, if this simplest case does not work for you,
then don't use lombok for it and write it out longhand", or make it
configurable (which makes the feature much more complicated).


 
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