Extension methods and API evolution

[Peter Levart]

On Saturday 19 December 2009 13:58:16 Mikael Grev wrote:
> On Dec 19, 2009, at 13:46 PM, Stefan Schulz wrote:
> >  And I am still
> > unconvinced about the benefit of extension methods, but maybe I missed
> > the win over static utility methods, except for being able to write
> > list.sort() instead of sort(list)
> 
> Having a utility method in another class breaks the logical path the
>  developer has to the method. The developer has the list object and want to
>  do a sort on it. There is no logical link between static utility methods
>  in say Collections and the objects that they can handle. The developer
>  must know this beforehand since it can't be explored with code completion
>  or similar IDE aids. One can help a bit by putting "soft" references to
>  classes containing utility methods in the JavaDoc, but those are not read
>  by most once you've learnt the API. So chances that developers familiar
>  with the List API will go back and read that soft link in Java 7 are not
>  very good.
> 
> So, having a method on the object itself is beneficial as it lowers the bar
>  for finding out that it exist.

A no-language-change alternative of that might be standardizing an annotation in the JDK 
platform that every IDE would add support for. For example:

package java.util;

@UtilityMethods({
    "java.util.Collections#binarySearch",
    "java.util.Collections#checkedList",
    "java.util.Collections#fill",
    "java.util.Collections#indexOfSubList",
    "java.util.Collections#lastIndexOfSubList",
    "java.util.Collections#replaceAll",
    "java.util.Collections#reverse",
    "java.util.Collections#rotate",
    "java.util.Collections#shuffle",
    "java.util.Collections#sort",
    "java.util.Collections#swap",
    "java.util.Collections#synchronizedList",
    "java.util.Collections#unmodifiableList"
})
public interface List<E> extends Collection<E> {
...


This way you give the author of the interface the opportunity to enumerate utility static 
methods he/she finds most appropriate.

I know that this would satisfy me.

Peter