Immutable collection values

[David Bruant]

Le 09/11/2014 15:07, Jussi Kalliokoski a écrit :
> I figured I'd throw an idea out there, now that immutable data is 
> starting to gain mainstream attention with JS and cowpaths are being 
> paved. I've recently been playing around with the idea of introducing 
> immutable collections as value types (as opposed to, say, instances of 
> something).
>
> So at the core there would be three new value types added:
>
> * ImmutableMap.
> * ImmutableArray.
> * ImmutableSet.
Why would both Array and Set be needed?

> We could also introduce nice syntactic sugar, such as:
>
> var objectKey = {};
>
> var map = {:
>   [objectKey]: "foo",
>   "bar": "baz",
> }; // ImmutableMap [ [objectKey, "foo"], ["bar", "baz"] ]
>
> var array = [:
>   1,
>   1,
>   2,
>   3,
> ]; // ImmutableArray [ 1, 2, 3, 4 ]
>
> var set = <:
>   1,
>   2,
>   3,
> >; // ImmutableSet [ 1, 2, 3 ]
>
> The syntax suggestions are up to debate of course, but I think the key 
> takeaway from this proposal should be that the immutable collection 
> types would be values and have an empty prototype chain.
I find ":" too discrete for readability purposes. What about # ?
That's what was proposed for records and tuples (which are pretty much 
the same thing as ImmutableMap and ImmutableSet respectively)
http://wiki.ecmascript.org/doku.php?id=strawman:records
http://wiki.ecmascript.org/doku.php?id=strawman:tuples
#SyntaxBikeshed

> I think this would make a worthwhile addition to the language, 
> especially considering functional compile-to-JS languages. With the 
> syntactic sugar, it would probably even render a lot of their features 
> irrelevant because the core of JS could provide a viable platform for 
> functional programming (of course one might still be happier using 
> abstraction layers that provide immutable APIs to the underlying 
> platforms, such as DOM, but then that's not a problem in the JS' 
> domain anymore).
It would also open the possibility of a new class of postMessage sharing 
(across iframes or WebWorkers) that allows parallel reading of a complex 
data structure without copying.

A use case that would benefit a lot from this would be computation of a 
force-layout algorithm with real-time rendering of the graph.

David