Shape objects

[Andrea Giammarchi]

StructType never really got a chance:
https://developer.mozilla.org/en-US/docs/Mozilla/js-ctypes/js-ctypes_reference/StructType

but it's also easy to have those kind of shapes in userland:

```js
const shape = definition => {
  const keys = Reflect.ownKeys(definition);
  const key = k => keys.includes(k);
  function type(key, i) {
    var expected = definition[key];
    var current = this[key];
    return typeof current === 'object' ?
      (!expected ||
        current instanceof expected) :
      expected(current) === current;
  }
  return class Shape {
    constructor(details) {
      const k = Reflect.ownKeys(details);
      if (
        k.length !== keys.length ||
        !k.every(key) ||
        !k.every(type, details)
      )
        throw new TypeError('wrong shape: ' + k);
      Object.freeze(Object.assign(this, details));
    }
  }
};
```

Regards


On Sat, Jun 16, 2018 at 9:56 AM, Cyril Auburtin <cyril.auburtin at gmail.com>
wrote:

> I wish JS had Shape objects, which would not only ease performance
> optimization for the benefit of JS engines (https://youtu.be/5nmpokoRaZI?
> t=871), but also helps for validation, like an interface
>
> ```js
> shape Point { x: Number, y: Number, name: String };
>
> const p = Point({x: 1, y: 2, name: 'foo'})
>
> const p = Point({x: 1, y: 2, naem: 'foo'}) // throws
> ```
>
> That object would have its properties immutable
>
> I think proposal-first-class-protocols (https://github.com/
> michaelficarra/proposal-first-class-protocols/issues/27#
> issuecomment-386975099) could more or less directly do that feature
>
>
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