Proposal: Collection Literals (original) (raw)

Neal Gafter neal at gafter.com
Tue Mar 31 01:16:26 PDT 2009

How does the syntax distinguish between an initializer for an array of sets, and an initializer for an array of arrays?

On Tue, Mar 31, 2009 at 1:13 AM, Joshua Bloch <jjb at google.com> wrote:

Mark, Thanks for reading the proposal. Inferring the right side from the left is called "target typing," and with one small exception, Java doesn't do it.  My proposal uses existing type inference rules, and allows you to use collection literals in in any reasonable context.  Besides the right hand side of assignments, this includes use as a method or constructor parameter (e.g., new HashSet({"Larry", "Moe", "Curly"}), before a dot (e.g., [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 9].size()), and elsewhere.  We don't have to further complicate Java's already complicated type inference logic to make this work; instead, we take advantage of the rules that are already there.

Josh On Tue, Mar 31, 2009 at 12:56 AM, Mark Thornton <mthornton at optrak.co.uk>wrote:

Joshua Bloch wrote:

The method invocations (Collections.unmodifiableList(Arrays.asList) are just noise. With list literals, it would look like this:

 final List piDigits = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 9];

By substituting curly braces for the square brackets, you get a set literal in place of a list:  final Set primes = { 2, 7, 31, 127, 8191, 131071, 524287 }; Would it be possible to infer the type of the RHS from the left (and thus also avoid Neal's issue with generics). You could then use {} for both lists and sets, and not need the odd syntax for an empty map. Thus: List emptyList = {}; Set emptySet = {}; Map<String, String> emptyMap = {}; Regards, Mark Thornton

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