JEP 186: Collection Literals

Jonathan C. Ross Jonathan.Ross at
Fri Jan 17 11:35:13 PST 2014

On Jan 16, 2014, at 6:46 PM, Zhong Yu <zhong.j.yu at> wrote:

> So are we going to allow
>    Person find()
>        ...
>        return "Paul";
> or
>    void save(Person person){ ... }
>    ...
>    save("Paul");
> ?
> This sound too dangerous. It most likely will hurt readability.

Dangerous?  Applied judiciously, it would be no worse than primitive autoboxing, which I definitely think aids readability.  If it was implemented naively, it would perhaps be dangerous for performance (just like primitive auto boxing).  But with proper byte code support (perhaps John Rose’s value-type approach?), one could eliminate the expense of both user-defined and intrinsic autoboxing.  Otherwise I would see no danger.  If you are afraid of syntactic ambiguities, you could require that the r.h.s. is a tuple literal, so:

        Person p = ( “Paul” );

(substitute your brackets of choice.  I have grown accustomed to Python and Scala’s parentheses for tuples, so that is my preferred notation. Curly braces would also make sense given the precedent of array initializers and C++’s initializer_list).

Given this literal assignment syntax, I think automatically mapping the tuple elements to constructor arguments would lead to a very nice coding experience indeed (c.f. initializer_lists in C++11 in absence of initializer_list constructors). I don’t see any situation where it would lead to ambiguities or lack of clarity.

>> works for me as well.  But is it really necessary if you can just write:
>>        Map<String, Integer> m = ImmutableMap.of((“First”,1), (“Second”, 2));
> How about using an infix operator, which saves two symbols per tuple.

In this example I had envisioned it actually being an array of pairs being passed in, but I guess you could add the ( . : . ) or ( . -> . ) shorthand for pairs too.  Ooh…. named arguments anyone?


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