Proposal: Allow a single-parameter method to be used as an infix operator

[Joseph D. Darcy]

The call for proposals period ended several weeks ago; this proposal is 
thus overdue and will not be considered.

-Joe

Elias Ross wrote:
> AUTHOR(S): Elias Ross
>
> OVERVIEW
>
> FEATURE SUMMARY: Allow a single-parameter method to be used as an
> infix operator. Expressions like "object1.method(object2)" could be
> replaced with an easier-to-read expression "object1 method object2".
> This allows for easier to read code such as "a equals b" instead of
> "a.equals(b)". This idea borrows from Scala, although this proposal
> limits the complexity.
>
> MAJOR ADVANTAGE: Since Java does not allow for operators or operator
> overloading, all idiomatic expressions, such as "a.equals(b)", or
> "a.contains(b)" must be written using dots and parenthesis.
>
> MAJOR BENEFIT: Improvement in clarity for many idioms.
>
> MAJOR DISADVANTAGE: Obviously, code with this feature would look quite
> different than code without. Thus, I imagine it would look quite
> inconsistent to have both used in the same codebase. Also, it's not
> clear why, in the case of "object1 equals object2", when "object1" was
> null, a NullPointerException should be thrown. It also may seemingly
> collide with the "instanceof" operator.
>
> It would potentially encourage increased use of single parameter methods.
>
> ALTERNATIVES: None.
>
> EXAMPLES
>
> SIMPLE EXAMPLE:
>
> boolean eq = "a" equals "b";
>
> ADVANCED EXAMPLE: Show advanced usage(s) of the feature.
>
> "abc" substring 1 matches "b."; // true
> (new BigInteger(10) divide new BigDecimal(2)).longValue(); // 5
>
> // The following would not compile
> "abc" substring(1,2) equals "b";
>
> DETAILS
>
> SPECIFICATION:
>
> Modification to
> http://java.sun.com/docs/books/jls/second_edition/html/syntax.doc.html
>
> Expression2Rest:
> 	{Infixop Expression3}
> +	{Identifier Expression}
> 	Expression3 instanceof Type
>
> The "Identifier" refers to a single parameter method belonging to a
> class or instance, and "Expression" here evaluates to the argument
> passed to this method.
>
> COMPILATION: The compiler would treat the expression as a method call.
>
> TESTING: Testing would be done to validate the grammar and conflict
> with the "instanceof" operator.
>
> LIBRARY SUPPORT: None.
>
> REFLECTIVE APIS: None.
>
> OTHER CHANGES: None.
>
> MIGRATION: Code needs no migration. However, it might be nice to have
> a tool to "clean up" existing code.
>
> COMPATIBILITY
>
> BREAKING CHANGES: None.
>
> EXISTING PROGRAMS: Should continue to work.
>
> REFERENCES
>
> EXISTING BUGS: Unknown.
>
> URL FOR PROTOTYPE (optional):
>
>