Bug Report

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🕗 Version & Regression Information

This changed between versions 3.3.3 and 3.5.1, and it keeps the behavior since then to the current latest version (at least 4.7.3).

⏯ Playground Link

Playground link with relevant code

💻 Code

class Test {
  a = '';
  b = 0;

  test() {
    const a: this['a'] = '';        // ok
    const b: this['b'] = 0;         // ok
    const c: Test['a' | 'b'] = '';  // ok
    const d: this['a' | 'b'] = '';  // fail
  }
}

🙁 Actual behavior

Type 'string' is not assignable to type 'this["a"] & this["b"]'.
  Type 'string' is not assignable to type 'this["b"]'.
    Type 'string' is not assignable to type 'number'.(2322)

🙂 Expected behavior

I expect this['a' | 'b'] to be string | number in this example, thus accepting the assignment of '' to it, just like Test['a' | 'b'].