Why does this compile!!??

[blendsdk]

Hi,

I was wondering why the code below compiles fine!
The compiler should complain for the last two lines, not?

interface ViewConfig {
    width?:number;
    height?:number;
}

interface ToolbarConfig {
    size?:number
}

class View implements ViewConfig {
    width:number;
    height:number;
    constructor(config:ViewConfig) {

    }
}

class Toolbar extends View implements ToolbarConfig {
    size:number;
    constructor(config:ToolbarConfig) {
        super(config);
    }
}


var myToolbar = new Toolbar('should not compile');
var myToolbar = new Toolbar(9999);

[carltonf]

Aren't all properties in the interface are optional? The it's ok that they are not there.
See http://www.typescriptlang.org/Handbook#interfaces-optional-properties

Quote: "The advantage of optional properties is that you can describe these possibly available properties while still also catching properties that you know are not expected to be available."

[RyanCavanaugh]

It's a structural type system, so an interface with all optional properties is assignable from anything.

This is a known pain point; see #391.