Convert data properties to private by default

[mlhaufe]

Data properties should not be publicly accessible by default. A trait must be defined to expose the desired properties.

This will enable Brevity to support the Uniform access principle. Additionally this will enable better encapsulation and Representation Independence.

const PointData = data({
    Point2: { x: Number, y: Number },
    Polar2: { rho: Number, theta: Number }
});

const PrintTrait = trait('print', {
    Point2({ x, y }) { return `Point2(${x}, ${y})` },
    Polar2({rho, theta}) { return `Polar2(${rho}, ${theta})` }
})

const XTrait = trait('x', {
    Point2({x}) { return x },
    Polar2({rho, theta}){ return rho * Math.cos(theta) }
})

const YTrait = trait('y', {
    Point2({y}) { return y },
    Polar2({rho, theta}) { return rho * Math.sin(theta) }
})

const Point = complect(PointData, [XTrait, YTrait, PrintTrait])

const {Point2, Polar2} = Point()

Point2(12, 5).x()

Polar2(5, 167).x()

Note this will subsume the derived property field of data:

Before:

const EmployeeData = data({
    Employee: {
        firstName: String,
        lastName: String,
        fullName: {
            guard: String, // Optional
            get() { return `${this.firstName} ${this.lastName}` }
        }
    }
})

const {Employee} = complect(EmployeeData)()

const johnDoe = Employee('John', 'Doe')

johnDoe.fullName === 'John Doe'

After:

const EmployeeData = data({
    Employee: { firstName: String, lastName: String }
})

const FullNameTrait = trait('fullName', {
    Employee({firstName, lastName}) { 
        return `${this.firstName} ${this.lastName}`
    }
})

const {Employee} = complect(EmployeeData, [FullNameTrait])()

const johnDoe = Employee('John', 'Doe')

johnDoe.fullName === 'John Doe'

Destructuring

Currently destructuring is allowed on complected instances intuitively as follows:

const disk = Disk({ position: [0, 0], velocity: [1, 3], radius: 1, item: 'apple' });

const [position, velocity, radius, item] = disk;

const { position, velocity, radius, item } = disk;

With the suggested change these would become function references, which seems to imply that they might need to be bound to the instance, otherwise an alternative form may be desirable.