`this` needs an explanation for the example given in `this-based type guards`

[tonyeung]

class FileSystemObject {
    isFile(): this is File { return this instanceof File; }
    isDirectory(): this is Directory { return this instanceof Directory;}
    isNetworked(): this is (Networked & this) { return this.networked; } <- what is *this* in (Networked & this)
    constructor(public path: string, private networked: boolean) {}
}

In the example above, I understand that the type guard checks if the object has a Network object and this is defined.
However, aside from the Network interface kind of just hanging out there (which is something else I do not understand), I'm not sure what this as pointed out in the code sample above is supposed to point to.

I've asked around with some people who write TS daily and I'm getting WTF? looks like I'm not even writing typescript...

[mhegazy]

currently http://www.typescriptlang.org/docs/release-notes/typescript-1.8.html#this-based-type-guards is the most documentation we have. we need an entry in the type guard section for it.

[tonyeung]

I understand that the statement means "if my type is an intersection of Networked and my type (this), return the instance of Networked that I have", now. I don't understand what the point of intersection operators are for other than for mixins and now type guards.

[mhegazy]

the second this is the this type (see http://www.typescriptlang.org/docs/handbook/advanced-types.html#polymorphic-this-types); it refers to the type of the containing class instance, FileSystemObject in this case, or one of its descendants that the function was invoked on.

for instance:

class Base {
   getThis(): this { return this; }
}

class Derived extends Base {
}

var b: Base;
var d: Derived;

b.getThis() // returns Base
d.getThis() // returns Derived

[tonyeung]

thank you. your reply helps a lot. should I keep this issue open or should it be closed, now that I understand the statement?

[mhegazy]

yes please.

[tonyeung]

I'm assuming you want it closed?

[mhegazy]

:). no i meant to leave it open. if you do not mind.

[tonyeung]

ah, sorry about that. Where should I go if I have questions about the language?

[mhegazy]

For general questions StackOverflow would be the best place. check out https://github.com/Microsoft/TypeScript/wiki/FAQ as well.

For compiler/language bugs: https://github.com/Microsoft/TypeScript
For documentation bugs, https://github.com/Microsoft/TypeScript-Handbook