State of the Lambda

[John Rose]

On Jul 7, 2010, at 2:56 PM, Joshua Bloch wrote:

> I'm a little bit worried that method references with receiver variables do
> an copy. ... A possible solution is to require such receiver
> variables to be (implicitly) final.

This is one of those times where syntax might imply something deep about an expression.  Brian's sketch uses a prefix "#" to introduce a method lifted to a function (and perhaps partially applied to a receiver).

The prefix looks like it might govern the evaluation of the expression to the right.  An infix operator would much more clearly express that the left hand side of the expression (at least) is evaluated in the normal left-to-right order of Java expressions.  (Some infix operators, ?: && || have special rules for evaluation order, but it only applies to the right of the operator.)

An infix formulation would make it clearer that the qualifier LHS is a normal expression:

  foo # bar
  baz[++n].bang() # bar

This means that foo#bar is not equivalent to { (T x) -> foo.bar(x) } if foo contains side effects or is affected by them.

-- John

P.S. FWIW, I prototyped the foo#bar syntax as a test for JSR 292, which includes an extended 'ldc' bytecode which can materialize arbitrary method constants.  See the bottom of the patch for a unit test file which exercises a similar syntax.
  http://hg.openjdk.java.net/mlvm/mlvm/langtools/file/tip/meth-ldc-6939203.patch