SetOf(type) and other collection checkers

[callumlocke]

What about SetOf(type), like ArrayOf but for ES6 sets?

Maybe also MapOf(keyType, valueType)?

This also got me thinking about extensibility... for example, if I am using an a custom/library-provided collection type like Immutable.OrderedSet, is there some way I could define my own ImmutableOrderedSetOf(type) (which I could then compose with other built-ins like Optional or ArrayOf(), etc)?

Maybe extensibility could be provided with a 'custom' type checker, which lets you supply a callback to examine the value in a custom way, like this:

import {Custom} from 'decorate-this';

const ImmutableOrderedSetOf = Custom((value, type) => {
  return value instanceof Immutable.OrderedSet && value.every(item => {
    return item instanceof type;
  });
});

@param(ImmutableOrderedSetOf(String))
function (strings) {
  // ...
}

(I don't actually know if this would work, just an idea.)

[mako-taco]

I do eventually want to support custom types. For now, I will probably just add SetOf, MapOf.

I will think on the API for a custom type checker afterwards. I could just expose Validator and ValidatorResult which I use internally, but they are a little confusing, and usually overkill for simple types.

[mako-taco]

I think this will get us by.

const ImmutableMap = KeyedCollection(Immutable.Map, map => map.toObject());
const ImmutableListOf = TypedCollection(Immutable.List, list => list.toArray());

class T {
    @param(ImmutableMap({key: String, val: String}))
    doThing() {
    }

    @param(ImmutableListOf(Number))
    doOtherThing() {
    }
}

KeyedCollection takes two arguments, a constructor/class and a transformation function. It returns a function which takes a type.

• The transformation function must return a plain Object

TypedCollection takes two arguments, a constructor/class and a transformation function. It returns a function which takes a type.

• The transformation function must return either an Array or an Object.
• The returned value will be iterated over with a for...of loop
• Each member of the value will be validated against the type

@callumlocke any comments?

[callumlocke]

looks great