records.ts

class Message {
    greeting: string;
    body: string;
    data: number;

    constructor(greeting: string, body: string, data: number) {
        this.greeting = greeting;
        this.body = body;
        this.data = data;
    }
    //already sucks - triple repetition
}

type Greeting = Message & { name: string;}

let m: Message = new Message("hey", "im a message", 42);

function doActualStuff(g: Greeting): void {
    console.log(g.name);
}

let g = m;
g.name = "Vasya";
g.anotherFieldNeededElsewhere = true;

doActualStuff(g);