list literal gotcha and suggestion

[Greg Brown]

I know this proposal has already been approved for inclusion in Java  
7, but it really seems like it might not be worth the effort. Wouldn't  
it be simpler to just add a varargs constructor to the collection  
classes? To me, this:

List<String> list = ["a", "b", "c"];

isn't much better than:

List<String> list = new ArrayList<String>("a", "b", "c");

With the improved type inference feature, declarations such as this  
will be even less verbose.

I recognize that maps are trickier, but I still think that this:

Map<String, Integer> map = new HashMap<String, Integer>(new  
AbstractMap.SimpleImmutableEntry<String, Integer>("a", 0),
	new AbstractMap.SimpleImmutableEntry<String, Integer>("b", 1),
	new AbstractMap.SimpleImmutableEntry<String, Integer>("c", 2));

is preferable to modifying the language for what (to me) seems like a  
fairly marginal use case.

Greg


On Sep 29, 2009, at 5:53 AM, Stephen Colebourne wrote:

> Over the 1.4million LOC codebase I work on, I found 12 set literals.
> We're not talking about large numbers. Interestingly, the majority of
> these were constants, and may be more common than list constants.
> There weren't any cases of parameter passing of a set literal.
>
> That said, I strongly dislike the confusion apparent here. We should
> avoid new puzzlers if possible. I'd prefer
>
> List<String> list = {"1", "2", "3"} - List literal
> Map<Integer, String> list = {1 : "1", 2 : "2", 3 : "3"} - Map literal
> No set literal
> (I don't think this conflicts with the array literals...)
>
> Perhaps there is also an argument for adding the static of methods to
> construct mutable Set/List:
>
> Set<String> set = HashSet.of("1", "2", "3");  // mutable set
> List<String> list = ArrayList.of("1", "2", "3");  // mutable list
> List<String> list2 = {"1", "2", "3"};  // immutable list
>
>
> One final thought. It would be possible to add a "method" to the  
> list literal:
>
> Set<String> set = {1, 2, 3}.toSet();  // immutable set
>
> This approach would handle additional interfaces too:
>
> SortedSet<String> set = {1, 2, 3}.toSortedSet();  // immutable  
> sorted set
> MultiSet<String> mset = {1, 2, 3}.toMultiSet();  // immutable
> multiset/bag (if added to JDK)
>
> Stephen
>
>
> 2009/9/29 Reinier Zwitserloot <reinier at zwitserloot.com>:
>> Scanning my codebase, they are quite rare. As the set literals are
>> causing rather a lot of pain, let's see some proof before going too
>> far down this road.
>>
>> Pain caused by set literals:
>>
>>  - ambiguity of {} - is that the empty set or the empty map?
>>  - set/list confusion.
>>  - the parser becomes quite a bit more complicated to handle the
>> difference between sets and maps.
>>
>>  --Reinier Zwitserloot
>>
>>
>>
>> On 2009/29/09, at 10:02, Mark Thornton wrote:
>>
>>> Reinier Zwitserloot wrote:
>>>> new HashSet<>(["a", "b", "c"]);
>>>>
>>>> is too much effort in the rare cases where you need to initialize a
>>>> set-typed parameter? This is java, not perl. Golfing isn't the end
>>>> goal.
>>>>
>>> Without scanning my codebase I wouldn't expect Set parameters and
>>> fields to be rare. I use Set's quite frequently.
>>>
>>> Mark Thornton
>>>
>>
>>
>>
>