// API
// A Union represents a union of terms.
-// A term is a type with a ~ (tilde) flag.
type Union struct {
- types []Type // types are unique
- tilde []bool // if tilde[i] is set, terms[i] is of the form ~T
+ terms []*term
}
// NewUnion returns a new Union type with the given terms (types[i], tilde[i]).
// of no types.
func NewUnion(types []Type, tilde []bool) *Union { return newUnion(types, tilde) }
-func (u *Union) IsEmpty() bool { return len(u.types) == 0 }
-func (u *Union) NumTerms() int { return len(u.types) }
-func (u *Union) Term(i int) (Type, bool) { return u.types[i], u.tilde[i] }
+func (u *Union) IsEmpty() bool { return len(u.terms) == 0 }
+func (u *Union) NumTerms() int { return len(u.terms) }
+func (u *Union) Term(i int) (Type, bool) { t := u.terms[i]; return t.typ, t.tilde }
func (u *Union) Underlying() Type { return u }
func (u *Union) String() string { return TypeString(u, nil) }
return emptyUnion
}
t := new(Union)
- t.types = types
- t.tilde = tilde
+ t.terms = make([]*term, len(types))
+ for i, typ := range types {
+ t.terms[i] = &term{tilde[i], typ}
+ }
return t
}
-// is reports whether f returned true for all terms (type, tilde) of u.
-func (u *Union) is(f func(Type, bool) bool) bool {
+// is reports whether f returns true for all terms of u.
+func (u *Union) is(f func(*term) bool) bool {
if u.IsEmpty() {
return false
}
- for i, t := range u.types {
- if !f(t, u.tilde[i]) {
+ for _, t := range u.terms {
+ if !f(t) {
return false
}
}
if u.IsEmpty() {
return false
}
- for _, t := range u.types {
- if !f(under(t)) {
+ for _, t := range u.terms {
+ if !f(under(t.typ)) {
return false
}
}
}
// Ensure that each type is only present once in the type list.
- // It's ok to do this check at the end because it's not a requirement
+ // It's ok to do this check later because it's not a requirement
// for correctness of the code.
// Note: This is a quadratic algorithm, but unions tend to be short.
check.later(func() {
x := tlist[i]
pos := syntax.StartPos(x)
// We may not know the position of x if it was a typechecker-
- // introduced ~T type of a type list entry T. Use the position
+ // introduced ~T term for a type list entry T. Use the position
// of T instead.
// TODO(gri) remove this test once we don't support type lists anymore
if !pos.IsKnown() {
}
u := under(t)
- if tilde[i] && !Identical(u, t) {
- check.errorf(x, "invalid use of ~ (underlying type of %s is %s)", t, u)
- continue // don't report another error for t
+ f, _ := u.(*Interface)
+ if tilde[i] {
+ if f != nil {
+ check.errorf(x, "invalid use of ~ (%s is an interface)", t)
+ continue // don't report another error for t
+ }
+
+ if !Identical(u, t) {
+ check.errorf(x, "invalid use of ~ (underlying type of %s is %s)", t, u)
+ continue // don't report another error for t
+ }
}
- if _, ok := u.(*Interface); ok {
- // A single type with a ~ is a single-term union.
- check.errorf(pos, "cannot use interface %s with ~ or inside a union (implementation restriction)", t)
+
+ // Stand-alone embedded interfaces are ok and are handled by the single-type case
+ // in the beginning. Embedded interfaces with tilde are excluded above. If we reach
+ // here, we must have at least two terms in the union.
+ if f != nil && !f.typeSet().IsTypeSet() {
+ check.errorf(pos, "cannot use %s in union (interface contains methods)", t)
continue // don't report another error for t
}
yu, _ := y.(*Union)
switch {
case xu != nil && yu != nil:
- // Quadratic algorithm, but good enough for now.
- // TODO(gri) fix asymptotic performance
- var types []Type
- var tilde []bool
- for j, y := range yu.types {
- yt := yu.tilde[j]
- if r, rt := xu.intersect(y, yt); r != nil {
- // Terms x[i] and y[j] match: Select the one that
- // is not a ~t because that is the intersection
- // type. If both are ~t, they are identical:
- // T ∩ T = T
- // T ∩ ~t = T
- // ~t ∩ T = T
- // ~t ∩ ~t = ~t
- types = append(types, r)
- tilde = append(tilde, rt)
- }
- }
- return newUnion(types, tilde)
+ return &Union{intersectTerms(xu.terms, yu.terms)}
case xu != nil:
if r, _ := xu.intersect(y, false); r != nil {
// intersect computes the intersection of the union u and term (y, yt)
// and returns the intersection term, if any. Otherwise the result is
// (nil, false).
+// TODO(gri) this needs to cleaned up/removed once we switch to lazy
+// union type set computation.
func (u *Union) intersect(y Type, yt bool) (Type, bool) {
under_y := under(y)
- for i, x := range u.types {
- xt := u.tilde[i]
+ for _, x := range u.terms {
+ xt := x.tilde
// determine which types xx, yy to compare
- xx := x
+ xx := x.typ
if yt {
- xx = under(x)
+ xx = under(xx)
}
yy := y
if xt {
}
return nil, false
}
+
+func identicalTerms(list1, list2 []*term) bool {
+ if len(list1) != len(list2) {
+ return false
+ }
+ // Every term in list1 must be in list2.
+ // Quadratic algorithm, but probably good enough for now.
+ // TODO(gri) we need a fast quick type ID/hash for all types.
+L:
+ for _, x := range list1 {
+ for _, y := range list2 {
+ if x.equal(y) {
+ continue L // x is in list2
+ }
+ }
+ return false
+ }
+ return true
+}
+
+func intersectTerms(list1, list2 []*term) (list []*term) {
+ // Quadratic algorithm, but good enough for now.
+ // TODO(gri) fix asymptotic performance
+ for _, x := range list1 {
+ for _, y := range list2 {
+ if r := x.intersect(y); r != nil {
+ list = append(list, r)
+ }
+ }
+ }
+ return
+}