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Newsgroups: comp.lang.java.programmer
Subject: new Java lambda syntax
Date: Thu, 08 Sep 2011 13:19:22 -0700
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Just thought some folks might be interested in this:


Date: Thu, 08 Sep 2011 16:07:03 -0400
From: Brian Goetz <brian.goetz@oracle.com>
To: "lambda-dev@openjdk.java.net" <lambda-dev@openjdk.java.net>


"This just in: the EG [Expert Group] has (mostly) made a decision on syntax.

After considering a number of alternatives, we decided to essentially
adopt the C# syntax.  We may still deliberate further on the fine points
(e.g., thin arrow vs fat arrow, special nilary form, etc), and have not
yet come to a decision on method reference syntax.

The C# syntax is:

    lambda = ArgList Arrow Body
    ArgList = Identifier
              | "(" Identifier [ "," Identifier ]* ")"
              | "(" Type Identifier [ "," Type Identifier ]* ")"
    Body = Expression
              | "{" [ Statement ";" ]+ "}"

Here are some examples of lambda expressions using this syntax:

    x => x + 1
    (x) => x + 1
    (int x) => x + 1
    (int x, int y) => x + y
    (x, y) => x + y
    (x, y) => { System.out.printf("%d + %d = %d%n", x, y, x+y); }
    () => { System.out.println("I am a Runnable"); }

The decision to choose this syntax was twofold:
   - The syntax scores "pretty well" on most subjective measures (though
has cases where it looks bad, just like all the others do).  In
particular, it does well with "small" lambdas that are used as method
arguments (a common case), and also does well with large
(multi-statement) lambdas.

   - Despite extensive searching, there was no clear winner among the
alternatives (each form had some good aspects and some really not very
good aspects, and there was no form that was clearly better than the
others).  So, we felt that it was better to choose something that has
already been shown to work well in the two languages that are most like
Java -- C# and Scala -- rather than to invent something new.

A compiler implementation should be available soon."