Using `if let` to check for equality

9

Problem of having expr is Pat(binding) is always about the scoping of those bindings (referring to [Pre-Pre-RFC] Reviving Refutable Let [Runoff] - #9 by kennytm again)

The JEP you mentioned is pretty short but skims lots of details, like how to determine the scope of y given x instanceof Type y. The actual implementation touches translation involving quite a number of constructs (&&, ||, !, ?:, if, while, do while, for), and contained some tests like these which I won't call them "boring" :upside_down_face:.

// Test for (!e).T = e.F
if (!(!(o1 instanceof String s) || !(o3 instanceof Integer in))){
    s.length();
    i.intValue();
}

// Test for (e1 ? e2 : e3).F contains intersect(e1.T, e3.F)
if (o1 instanceof String s ? true : !(o1 instanceof String s)){
} else {
    s.length();
}