JEP 186: Collection Literals

[Zhong Yu]

On Tue, Jan 14, 2014 at 7:17 PM, Per Bothner <per at bothner.com> wrote:
> On 01/14/2014 03:02 PM, Richard Warburton wrote:
>> Is there any real reason to restrict the proposal to implementing any
>> specific interface? It seems preferable to able to specify some kind of
>> recipe or factory for building an arbitrary concrete type out of a
>> collection literal.
>
> For example, one could define:
>
> T v = { e1, ..., en}
>
> as syntactic sugar for:
>
> TB tmp = T.make_builder();
> tmp.add(e1); ..; tmp.add(en);
> T v = tmp.build();

How is this any better than

    T.of(e1, ..., en);

? I don't see how the literal syntax helps code writers or code
readers in this case. List is too trivial for this discussion. If
people want literals for more complicated data structures, please
expand on those ideas in details.

Zhong Yu

>
> The type TB is inferred as the return type of make_builder.
> It may be the same as T, and TB.build is allowed to return
> the argument - perhaps after sealing it as immutable.
>
> [The following goes quite a bit beyond Collection Literals,
> and is probably not appropriate for Java, unless we come up
> with a very simple and general-purpose syntactic sugar.]
>
> If you're going that route, one might consider literals
> for non-collection classes as well.  These often need a
> string-based syntax.  For example:
>
> T#{literal[exp]text}
>
> could be syntactic sugar for:
>
> T.valueOf("literal"+(exp)+"text")
>
> Campl p4 has an interesting quotation syntax:
> http://caml.inria.fr/pub/docs/tutorial-camlp4/tutorial004.html
>
> Kawa has a quite flexible syntax:
>
> &T[prefix-exp1 ... prefix-expn}{literal&[exp]text}he
>
> http://srfi.schemers.org/srfi-108/srfi-108.html
>
> This syntax leads to a neat syntactic sugaring of ProcessBuilder:
>
> &`[out-to: "/tmp/msg"]{echo The directory is: &`{pwd}}
>
> This is equivalent to the shell command:
>
> echo The directory is: `pwd` >/tmp/msg
>
> http://per.bothner.com/blog/2014/Kawa-shell-programming/
> --
>         --Per Bothner
> per at bothner.com   http://per.bothner.com/
>