JEP 186: Collection Literals

[Remi Forax]

On 01/15/2014 11:02 PM, Brian Goetz wrote:
> If we were to do something like that (BTW, something very similar was in
> one of the Collection Literal proposals from the Coin timeframe), we'd
> also want to upgrade the indexes to long; 2B is just too low a limit for
> the next 20 years.  Which also means that using ... in the initializer
> is a no-go.

unless you have a way to create big array which is compatible with small 
array,
anyway as Per mention the compiler will hit the maximum number of 
bytecodes (65535) by method before even reaching a big index.

Rémi

>
> On 1/15/2014 2:50 PM, Timo Kinnunen wrote:
>> Hi,
>>
>>
>>
>>
>> Re: “Array literals (and, array types) are more of an oddity from today's
>> point of view; we should get rid of them if that were possible,
>> because their functions can be perfectly achieved with other general
>> purpose language devices.”
>>
>>
>>
>>
>> If it is at all possible, it’s possible through providing something that’s simpler and in all respects better than old arrays.
>>
>>
>> With one magical annotation, you could do:
>>
>>
>>
>> @Retention(RetentionPolicy.SOURCE)
>>
>> @interface SyntaxProvider {
>>
>> @Retention(RetentionPolicy.SOURCE) @Target(ElementType.METHOD) @interface ArrayInitializer {}
>>
>> @Retention(RetentionPolicy.SOURCE) @Target(ElementType.METHOD) @interface ArrayGetter {}
>>
>> @Retention(RetentionPolicy.SOURCE) @Target(ElementType.METHOD) @interface ArraySetter {}
>>
>> @Retention(RetentionPolicy.SOURCE) @Target(ElementType.METHOD) @interface ArrayLength {} }
>>
>>
>> Which allows:
>>
>>
>> interface ArraySyntaxProviderForMyClass {
>>
>>
>> // Allows: MyClass it = { myItem1, myItem2 };
>>
>> @SyntaxProvider.ArrayInitializer
>>
>> static MyClass containing(MyItem... items){
>>
>> return new MyClass(Arrays.asList(items)); }
>>
>>
>> // Allows: MyItem there = it[100_000_000_000_000L];
>>
>> @SyntaxProvider.ArrayGetter
>>
>> static MyItem getAt(MyClass that, long index){
>>
>> //TODO: Implement actual long indexing
>>
>> return that.items.get((int) index); }
>>
>>
>>
>> // Allows: MyItem another = it[1] = there;
>> @SyntaxProvider.ArraySetter
>> static MyItem setAt(MyClass that, long index, MyItem item){
>>
>> that.items.set((int) index, item); return item; }
>>
>>
>>
>> // Allows: long items = it.length;
>> @SyntaxProvider.ArrayLength
>> static long getLengthOfMyClass(MyClass it){
>>
>> return it.items.size(); }
>>
>>
>> This covers most of the usual array stuffs already. Lists, ArrayLists are doable. Add interleaved varargs at compile-time and that covers Maps and JSON:
>>
>>
>> // Allows: MyClass it = { "one", new MyItem(1), "two", new MyItem(2) };
>>
>> @SyntaxProvider.ArrayInitializer
>>
>> static MyClass createdFrom(String[] keys, MyItem... items){
>>
>> MyClass myClass = new MyClass(Arrays.asList(items));
>>
>> for(int i = 0, n = keys.length; i < n; i++) {
>>
>> myClass.index.put(keys[i], items[i]);
>>
>> }
>>
>> return myClass; }
>>
>>
>> Faking array[. . .] syntax by making it mean the same as calling somestaticmethod(array, . . .) covers indexing with multiple axis in one call, allowing sparse tables and continuous multi-dimensional arrays:
>>
>>
>> // Allows: MyItem item = myClass["clubs", 10];
>>
>> @SyntaxProvider.ArrayGetter
>>
>> static MyItem getAt(MyClass that, String id, int subId){
>>
>> return that.items.get(subId).index.get(id); }
>>
>>
>> // Allows: MyItem old = myClass["clubs", 10] = new MyItem(5);
>>
>> @SyntaxProvider.ArraySetter
>>
>> static MyItem setAt(MyClass that, String id, int subId, MyItem item) {
>>
>> return that.items.get(subId).index.put(id, item); // returns old item, if any, unlike arrays
>>
>> } }
>>
>>
>> class MyItem extends MyClass { int value;
>>
>> public MyItem(int i) {
>>
>> super(new ArrayList<>());
>>
>> this.value=i; } }
>>
>>
>> class MyClass implements ArraySyntaxProviderForMyClass {
>>
>> List<MyItem> items;
>>
>> Map<String, MyItem> index = new HashMap<>();
>>
>> public MyClass(List<MyItem> asList) { this.items=asList; } }
>>
>>
>>
>>
>> If some of the array syntax is to be reused, better reuse all of it to leave no doubt.
>>
>>
>> Is this the least expansive way of covering all of these cases or is there some other way that has an even smaller impact or footprint?
>>
>>
>>
>>
>>