TypeScript Version: nightly (2.2.0-dev.20161210)

Code

function test([a, b]: [number, number] | [string, string]) {
  if (typeof a === 'number') {
    b++
  }
}

Expected behavior:
b to be narrowed to number and the resulting code to throw no compiler errors

Actual behavior:
b has type number | string and thus the code throws a compiler error complaining that b++ can only apply to numbers