Re: [morph-developer] null as copy source

[Matt B. <gud...@ya...>]

Matt,
  Your proposal sounds fine to me, as long as we
realize we will have to fix some test cases that
expect a copy with a null source to fail.  :)

-Matt B

--- Matt Sgarlata
<Mat...@wh...> wrote:

> Matt Benson wrote:
> > A simplified use case:
> >
> > I have an object hierarchy of which certain
> classes
> > represent collections (but are not "Collection"s).
>  I
> > may build an object graph that needs to have
> another
> > graph copied to it.  Parts of the source graph may
> be
> > null, but for my purposes I need a copier that
> knows
> > how to copy null on the source graph to the
> collection
> > type on the destination graph by making it empty. 
> It
> > was a one-line change to BaseTransformer.copy() to
> > allow me to do this.  If you are not "married to"
> the
> > idea that null is NEVER a valid copy source, can
> we
> > let this change stand?  As far as I can see this
> is
> > the only way to completely correctly satisfy this
> > particular use case, so this indicates to me that
> > occasionally there may be a reason to allow this.
> >   
> That is exactly the use case I had not thought of. 
> The change sounds 
> perfectly valid to me :)
> 
> Given the use case you mention, I actually think we
> should take this 
> even further and remove the exception altogether. 
> If null can be a 
> valid source object (which your use case
> demonstrates that it is), then 
> there's no reason to throw an exception.  This would
> almost be like 
> throwing an exception if an empty collection or bean
> with no properties 
> was found, it just doesn't make a whole lot of
> sense.  So I propose this:
> 
>         if (source == null &&
> isAutomaticallyHandlingNulls()) {
>             return; // nothing to copy, so we're
> done
>         }
> 
> Matt S
> 
> > -Matt B
> >
> > --- Matt Sgarlata
> > <Mat...@wh...> wrote:
> >
> >   
> >> The idea behind a convert operation is you are
> >> transforming one object 
> >> into another object.  I think it can make sense
> to
> >> transform null to 
> >> "null" (a String containing 4 characters) or
> >> something else, so a source 
> >> of null on a convert operation makes sense.
> >>
> >> The idea behind a copy operation is you are
> taking
> >> information from one 
> >> object and copying that information to some other
> >> object.  A null by 
> >> definition is nothing, so to me it doesn't make
> >> sense that you're 
> >> copying nothing onto something.  I can't actually
> >> write down nothing, 
> >> it's the same as having not written anything at
> all.
> >>
> >> I'm not married to the idea that null sources are
> >> allowed for 
> >> conversions but not for copy operations, but I
> can't
> >> think of an example 
> >> where copying a null onto some other object would
> >> actually make sense.  
> >> I would expect this to be a programmer error, and
> so
> >> that is why a 
> >> TransformationException is thrown.
> >>
> >> Matt S
> >>
> >> Matt Benson wrote:
> >>     
> >>> Currently the Copier interface carries the
> >>>       
> >> implicit
> >>     
> >>> message that the source object cannot be null. 
> >>>       
> >> Should
> >>     
> >>> we persist in this assumption, or do we believe
> >>>       
> >> it's
> >>     
> >>> possible sometimes that null can be a legitimate
> >>>       
> >> copy
> >>     
> >>> source?
> >>>
> >>> -Matt B
> >>>
> >>>
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