Re: [morph-developer] null as copy source

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

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.

-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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