title: typescript initialize object with partial object literal
body: <p>I want to initialize an instance of a class with an object literal not containing all the elements in the class but whose elements are in the class.</p>
  
  <pre><code>class ATest{
      aStr:string;
      aNum:number;
  
      result(){return this.aStr + this.aNum;}
  }
  let test=new ATest;
  
  test={aStr:"hello",aNum:12};   // error, result() is missing in the object literal
  </code></pre>
  
  <p>What is the way to do that assignment exploiting the most of the validations of ts?</p>
  
  <pre><code>test=Object.assign(test,{aStr:"hello",aNom:12});
  </code></pre>
  
  <p>would work but then you miss the validation of the input fields - see aNom that's wrong but gets in</p>