cross-references within named argument lists

[@gavinking] A feature I have always planned on, that we’ve recently begin to discuss, including in #3850, is the ability to cross reference arguments within a named argument list, for example:

Panel {
    value label = Label { size = Size(50,10); },
    value button = Button {
        label = "Click me";
        size = Size(50,10); 
        onClick() => label.text="Hello!"; 
    };
}

We need at least two things:

1. to be able to assign a name to a listed argument, and
2. to be able to refer to previous arguments by the parameter name or assigned name within the body of subsequent arguments.

We may or may not need the following:

• to be able to assign a local name to an “anonymous” argument,
• to be able to freely declare something in the body of a named argument list that is not an argument (depends on #3604), and/or
• to be able to refer to later arguments by name.

[Migrated from ceylon/ceylon-spec#749]

[quintesse]

Personally I like proposal 2 better. Even though proposal 1 is perhaps more “expressive” or “powerful” I think it will make it easier to write complex code that’s hard to understand. With proposal 1 you’d have to understand more about the intricacies of value vs actual vs the already somewhat complex-ish rules of named arguments (using ; as a separator instead of , except for any iterable arguments at the end, etc). I think proposal 2 needs less “special knowledge” making things easier to read in general.

[luolong]

sorry for accidentally closing this issue … reopened it again…