Proposal: Indexing access syntax for Lists and Maps

Mark Thornton mthornton at
Mon Mar 30 06:51:06 PDT 2009

Shams Mahmood wrote:
> Hi Joe,
> Haven't used too many annotations in Java code. I had fiddled with the idea
> of Indexable (yes even I
> had come up with the same name - our vocabularies are so limited ;) ), but I
> decided otherwise for the
> following reasons:
> 1) Java traditionally has wanted to avoid operator overloading (Indexable
> means compiler providing
> operator support for Indexable marked classes). Although for each loops have
> special handling cases
> for Iterable types.
> 2) get/set implementation of Lists and Maps will need to change. In fact Map
> doesn't even have a
> set, so a new method will be added to the interface breaking backwards
> compatibility.
> Shams.
The advantage of using an annotation is that the List/Map interfaces 
DON'T need to change other than the addition of the annotation to 
specify the methods to be used for indexed get and set. So Map becomes 
something like:

interface Map<K,V> {
    @indexedGet V get(Object key);
    @indexedSet V put(K key, V value);
    // rest unchanged

interface List<E> {
    @indexedGet E get(int index);
    @indexedSet E set(int index, e element);

Implementations of these interfaces don't need to change at all. A 
marker interface could be used as well, but doesn't seem to me to be 
strictly necessary (I'll post some more suggestions on this later).

Mark Thornton

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