transpiler: constructor and typed field semantics

[tbosch]

1. Only allow assignments to fields in constructor and translate these assignment into constructor initializers
2. Make field declaration explicit through @FIELD annotation
3. Make const constructors in Dart through @CONST annotation

Example:

class Annotation {
  @FIELD('final name:String')
  @FIELD('final age:int')
  @CONST constructor(name:String, age:int) {
    this.name = 'Hello ' + name;
    this.age = age + 0;
  }
}

@Annotation('usage', 5)
class Foo {}

this needs to transpile to:

class Annotation {
  final String name;
  final int age;
  const Annotation(String name, int age): 
     name = 'Hello ' + name,
     age = age + 0;
}

@Annotation('usage', 5)
class Foo {}

[mhevery]

@vicb Please let us know when you can start working on it.

[vojtajina]

new syntax that we agreed on...

class Foo {

  @FINAL('bar,name,age')
  @CONST
  constructor(age: number, name: string) {
    this.bar:boolean = true;
    this.name:string = 'Hello ' + name;
    this.age = age;
  }
}

get transpiled into....

class Foo {

  final int age;
  final String name;
  final bool bar;
  const Foo(int age, String name) : bar = true, age = age, name = 'Hello ' + name {
    // Note how final fields have been hoisted into the "initializer", after the colon.
  }
}

[vicb]

What would be the purpose of the @FINAL here ? All fields have to be final with a constant constructor.

@FINAL could be useful for non-const ctor to force members to be final. What about @FINAL(['bar', 'name', 'age']) ? In a second step the final modifier could probably be added automatically by visiting the class. If we agree on this we should probably evaluate the effort of writing the "final transfomer" and if it is not too complex then skip the intermediate @FINAL. What do you think ?

side notes:

• age should probably be a num, see transpiler: number (js) should map to num (dart) #17
• I think that a const ctor could not have a body in Dart then the transpiled code from the previous post is not valid, there should be a ";" after the initializer list

[vicb]

@mhevery I want to fix #24 before and then I'll start working on this issue. Probably later today or tomorrow.

[vojtajina]

+1 for Making all fields final by default if the constructor is const

As for your sidenotes: yes, yes.