Proposal: Collection Literals

[Neal Gafter]

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<Integer> 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<Integer> 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<Integer> emptyList = {};
>> Set<Integer> emptySet = {};
>> Map<String, String> emptyMap = {};
>>
>> Regards,
>> Mark Thornton
>>
>>
>
>