TypeScript Version: 3.0.0-dev.20180712
Error: This condition will always return 'false' since the types 'A' and 'I' have no overlap.
TypeScript Version: 2.9.2
Error: Operator '===' cannot be applied to types 'A' and 'I'

Search Terms:
Operator '===' cannot be applied to types
This condition will always return 'false' since the types have no overlap.
Code

class A { 
  private field: string;
}
interface I { 
  pub: string;
}
class B extends A implements I { 
  pub: string;
}
let b = new B();
let a: A = b
let i: I = b;
if (a === i) { // on TS 2.9.2: Operator '===' cannot be applied to types 'A' and 'I'
// on TS 3.0.0-dev.20180712:  This condition will always return 'false' since the types 'A' and 'I' have no overlap.
  console.log('qq');
}

Expected behavior:
no error
Actual behavior:
error
Playground Link: link

Related Issues: no

This case found from real project. Class and interface may be implemented and extended by another class, and in this case this error is pointless.