JavaExamples

/// Java Examples

// Mutating immut set, `s` is immut
void foo(Set<String> s) {
  Set<String> new_s = s;
  new_s.add("x"); // ERROR
}

// Mutating immut set, `new_s` is immut
void foo(@Mutable Set<String> s) {
  Set<String> new_s = new HashSet<>(s);
  new_s.add("x"); // ERROR
}

// Mutating mut set
void foo(Set<String> s) {
  @Mutable Set<String> new_s = new HashSet<>(s);
  new_s.add("x"); // OK
}

// Type parameter mutability
void foo(Set<List<String>> s, List<String> l) {
  assert s.get(l) != null;
  List<String> v = s.get(l);
  l.add("x"); // ERROR
  v.add("x"); // ERROR
}

// Immut class and its members
class Person {
  String name;
  List<String> family;

  Person(String n, List<String> f) {
    this.name = n; // OK
    this.family = f; // OK
  }

  void setName(String n) {
    this.name = n; // ERROR
  }

  @Mutable List<String> getFamily() {
    return family; // ERROR
  }
}

void foo(Person p) {
  p.name = "Jenny"; // ERROR
  p.family.add("Jenny"); // ERROR
  p.family.getFamily().add("Jenny"); // OK
}

// Mut class and its members
@Mutable class Person {
  String name;
  List<String> family;

  Person(String n, List<String> f) {
    this.name = n; // OK
    this.family = f; // OK
  }

  void setName(String n) {
    this.name = n; // OK
  }

  List<String> getFamily() {
    return family; // OK
  }
}

void foo(Person p) {
  p.name = "Jenny"; // OK
  p.family.add("Jenny"); // OK
  p.family.getFamily().add("Jenny"); // ERROR
}