Re: [morph-developer] Open up access to setSource/DestinationClasses in BaseTransformer

[Matt S. <Mat...@wh...>]

Short answer: I think it's better to leave it protected in 
BaseTransformer and just override it to be public in ChainedConverter.

Long answer:

I don't think it’s appropriate for all transformers that extend from 
BaseTransformer to expose their source and destination classes as 
mutable properties. The source and destination classes are the contract 
that specifies what a transformer can do, and if an individual 
transformer wants to control this, it should be free to do so in a 
protected manner. An example of this would be the TextTransformer, which 
has a set number of text types it can handle.

But what if a user were to want to change the behavior of 
TextTransformer so that there are more or fewer types it could handle? 
Well, to add a new text type to TextConverter it would be necessary to 
subclass TextConverter anyway to implement the transformation. There is 
a stronger case for removing capability, for example if you had your own 
converter you wanted to handle char[] -> String conversions and so 
wanted to limit the TextConverter’s functionality by reducing the source 
and destination classes. Both of these use cases are somewhat artificial 
though because there is an even simpler solution: just change the order 
of the transformers in your SimpleDelegatingTransformer so that it gets 
chosen before TextConverter is even tried.

There certainly are cases where transformers want their source and 
destination classes to be public, and they can override the definition 
in BaseTransformer. BasePropertyNameCopier does this so that 
PropertyNameMatchingCopier and PropertyNameMappingCopier can be used for 
simple transformations without blocking other transformers from being 
used in a SimpleDelegatingTransformer. ChainedConverter sounds like 
another place where it’s reasonable to make the source and destination 
classes mutable.

Matt S

Matt Benson wrote:
> I can't see a reason why we can't do this.  One use
> case I am seeing is with a ChainedConverter, being
> able to set the source and/or destination classes on
> the chain components helps to direct the flow of the
> chained transformation.
>
> WDYT?
>
> -Matt B
>