Add support for types

[matthewp]

This adds support for types as defined by can-data-types. This is
dependant on a new minor version of can-data-types with these methods
added.

Strict types

This is provided by type: types.check(Type) or by type: Type for the case of native types like Date, String, Number.

Here's an example usage:

class Person extends DefineClass {
  static define = {
    age: {
      type: Number
    },
    birthday: {
      type: types.check(Date)
    }
  }
}

In the above, it will throw if a non-number age is provided or a
non-Date birthday.

Maybe types

This is provided by type: types.maybe(Type). This is a strict type,
but null and undefined` are also allowed.

class Person extends DefineClass {
  static define = {
    age: {
      type: Number
    },
    birthday: {
      type: types.maybe(Date)
    }
  }
}

Convert / coerce

This is provided by type: types.convert(Type) and accepts any type,
which is attempted to be coerced to Type.

class Person extends DefineClass {
  static define = {
    age: {
      type: types.convert(Number)
    }
  }
}

let person = new Person({ age: "23" });
// person.age -> 23

Maybe convert

Like types.maybe() but attempts to convert. Values of null and
undefined will be left alone.

Required properties

This pull request also adds a required property. When set to true a
value must be provided upon instantiation.

class Person extends DefineClass {
  static define = {
    age: {
      type: Number,
      required: true
    }
  }
}

let person = new Person();
// Throws with a message about age being required.

Weird things

• This is built on top of canReflect.convert(). It's a little weird that strict types are implemented throw a convert() function. It's infrastructure so I tend to think this doesn't matter as much.

Pending

• Should convert be coerce and maybeConvert be maybeCoerce?
• Currently instantiation happens upon construction. For custom elements
  this needs to be delayed until connectedCallback. This will be added
  in a followup issue.
• type: Primitive is not yet implemented.
• prop: Type is not yet implemented. Should it be?

Closes #3

[phillipskevin]

This is built on top of canReflect.convert().

Where does this happen? Or is this not in the code yet?

Should convert be coerce and maybeConvert be maybeCoerce?

I prefer convert due to how some people have trouble spelling coerce.

Currently instantiation happens upon construction. For custom elements
this needs to be delayed until connectedCallback. This will be added
in a followup issue.

Is this something that can-define-class should be responsible for? can-stache-define-element will use the define function directly to do the instantiation in the connectedCallback.

[phillipskevin]

Can we add the name of the type to this error message?

[matthewp]

I'm not sure that we should, the required property is unrelated to the type. A property can be required without having an explicit type. I think adding the type might make it confusing, but I also see how it might be useful.

[phillipskevin]

Sorry, I meant the class, like canReflect.getName(this).

[matthewp]

Oh I see, so if you are rendering a template with many components you can figure out which one it throwing the error? Makes sense. Probably should check for localName possibly even.

[matthewp]

Where does this happen? Or is this not in the code yet?

Already in the code ported from can-define. https://github.com/canjs/can-define-class/blob/f9ba6177fe849d135979b2e0f479e40b6f4109aa/define.js#L623

Is this something that can-define-class should be responsible for? can-stache-define-element will use the define function directly to do the instantiation in the connectedCallback.

Not sure how that's possible... the symbols and everything else on the prototype needs to be there. So it needs to be used as a class mixin. Plus I definitely think can-define-class should be useable directly on an HTMLElement.

[matthewp]

Follow up issues here:

• Delay instantiation until connectedCallback when derived from HTMLElement #31
• Make sure passing a derived DefineClass as the definition works #33
• Allow passing primitive constructors as type #32

[matthewp]

I'm going to do a prerelease of can-data-types and then update this.