I assume Dart refers to the same variable since: 1) Dart doesn't have threads, it has isolates (where memory is not shared). So no variable modifications here.

I assume Dart refers to the same variable since: 1) Dart doesn't have threads, it has isolates (where memory is not shared). So no variable modifications here. 2) Dart will promote a variable as not null after a non-null check only if it cannot be modified elsewhere, ie, the variable is final (can't be modified once assigned), or there's no other reference to it.