Consider use x.getClass as a null check

[retronym]

These are semantically equivalent:

if (x eq null) throw new NullPointerException() //1
if (x eq null) throw null //2
x.getClass //3

We use option 2 in our null checks for the outer pointer in inner class constructors. I just noticed that javac used option 3 when spinning up a lambda based on an instance method reference.

    //  0: aload_0
    //  1: astore_1
    //  2: aload_1
    //  3: dup
    //  4: invokevirtual #3                  // Method java/lang/Object.getClass:()Ljava/lang/Class;
    //  7: pop
    //  8: invokedynamic #2,  0              // InvokeDynamic #0:x:(LTest;)LTest$FI1; (invokevirtual Test.bar:(Ljava/lang/Object;Ljava/lang/Object;)V)
    // 13: areturn
FI1 a1() { Test t1 = this; return t1::bar; }

[sjrd]

That would be bad for performance in Scala.js. That said, it wouldn't be hard to optimize a call to getClass in statement position into a null check in our optimizer, if you choose to go that route.

[lrytz]

we could just do that in our backend, so it wouldn't reach scala.js codegen

[dwijnand]

Curious, but sounds like the status quo is good enough or better.