Monday, November 12, 2012

Notes from November 5th Language Design Meeting

Dart engineer Bob Nystrom has posted the notes from the November 5th language design meeting. He writes:

Here's my notes from last week's meeting. There's no meeting this week, so this will have to tide you over. :)

NoSuchMethod and ()

Lars brought up bug 6428.

In Dart, if you call foo(), you get a noSuchMethod error for method "foo". If you call (foo)(), you get noSuchMethod error for getter "foo". This is how the language is specified and it's the behavior the designers expected, but dart2js doesn't currently do it correctly, and the behavior may be unintuitive.

Gilad says he'll look at the bug.


Lars: If you want to forward something with optional params. Right now you cannot.
Gilad: I want to look at it some more. I'd like to reuse mechanism.
Bob: We realized this in Seattle shortly after the new signature stuff came out. After some discussion, our guideline is just "never use that question mark operator thing" since it breaks forwards.
Lars: The problem is not the question mark operator. Cannot cleanly do pass-along in noSuchMethod either.
Gilad: Question operator was part of solution but doesn't work in all cases.

There's more context on this here:

Configuration-specific code

Lars: We handle this in the core libraries using patch but we don't definitely don't want to expose that to the world. We need a solution. Proposals are welcome, but would really like something that's extremely simple.

"abstract" modifier

Gilad: It's gone, right?
Bob: Is it optional or gone?
Lars: We originally planned to make it optional but we discussed it some more. If you make it optional, you get stylistic wobble. Some people will use it and some won't. If it's optional, we couldn't find good places where it made sense to put it in.
Lars: So decision as of today is that abstract is not allowed for members.

Call operator and call() method on SendPort

In the spec, when you do foo(), if foo is an object with a call() method, it desugars to invoking that. Unrelated, SendPort has a method named call().

Gilad: Don't want to be able to call on a SendPort using just parentheses. Should we renamed the method, or consider changing the language to have an actual operator ()?  There's a lot of moving parts so not sure if we want to do this.
Lars: The operator would be more symmetric with how its called. Is this is a pressing issue?
Gilad: Presumably it will get implemented soon and people may start using the current semantics.
Lars: Can you file a bug to track it?

Wrong number of type arguments

Gilad: We intended to change it from an error to a warning.
Lars: What are the semantics?
Gilad: If it has the wrong number of type arguments, it will throw at the constructor.

Shadowing setters

Lars: Have an open issue about pairwise shadowing of fields.

Here's an example. Start with this:

    class Foo {
      var bar;

      method() {
        var bar = 1;
        bar = 2; // assign to local

Now change it to:

    class Foo {
      var bar;

      method() {
        final bar = 1; // var -> final
        bar = 2; // call setter!

We should look at some sort of pairwise shadowing. Otherwise it's too surprising.

We all agree this should be solved. We can work on this when we are in person.


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