ClassSpec ClassSpec::operator&(const ClassSpec& rhs) const {
auto const& lhs = *this;
if (lhs <= rhs) return lhs;
if (rhs <= lhs) return rhs;
assertx(lhs.cls() && rhs.cls());
// If neither class is an interface, their intersection is trivial.
if (isNormalClass(lhs.cls()) && isNormalClass(rhs.cls())) {
return Bottom;
}
// If either is an interface, we'd need to explore all implementing classes
// in the program to know if they have a non-empty intersection. Instead,
// we'll just try to take the "better" of the two. We consider a normal
// class better than an interface, because it might influence important
// things like method dispatch or property accesses better than an interface
// type could.
if (isNormalClass(lhs.cls())) return lhs;
if (isNormalClass(rhs.cls())) return rhs;
// If they are both interfaces, we have to pick one arbitrarily, but we must
// do so in a way that is stable regardless of which one was passed as lhs or
// rhs (to guarantee that operator& is commutative). We use the class name
// in this case to ensure that the ordering is dependent only on the source
// program (Class* or something like that seems less desirable).
return lhs.cls()->name()->compare(rhs.cls()->name()) < 0 ? lhs : rhs;
}
static folly::Optional<ClassInfo> commonAncestor(ClassInfo a,
ClassInfo b) {
if (!isNormalClass(a.get()) || !isNormalClass(b.get())) return folly::none;
if (auto result = a.get()->commonAncestor(b.get())) {
return ClassInfo(result, ClassTag::Sub);
}
return folly::none;
}
ClassSpec ClassSpec::operator|(const ClassSpec& rhs) const {
auto const& lhs = *this;
if (lhs <= rhs) return rhs;
if (rhs <= lhs) return lhs;
assertx(lhs.cls() && rhs.cls());
// We're unwilling to unify with interfaces, so just return Top.
if (!isNormalClass(lhs.cls()) || !isNormalClass(rhs.cls())) {
return Top;
}
// Unify to a common ancestor if possible.
if (auto cls = lhs.cls()->commonAncestor(rhs.cls())) {
return ClassSpec(cls, ClassSpec::SubTag{});
}
return Top;
}