title: Typescript map.get method returns undefined when my key is of some interface type
body: <p>I have a main.ts file which is having a map with key as interface <code>dr</code> and value as string. when i try to get some value from the map using <code>get</code> it returns undefined .Below is my code:</p>
  <pre><code>interface dr {
  a: string;
  b: string;
  }
  
  let myMap = new Map&lt;dr,string&gt;();
  myMap.set({ a: 'foo', b: 'bar' }, `this is my map`);
  
  export default (a:string,b:string): string =&gt; {
  return myMap.get({ a: a, b: b })!;
  
  };
  </code></pre>