Replaced Exists/Forall with new Find method in set

set/set.go

@@ -67,28 +67,27 @@ func (s Of[T]) Equal(other Of[T]) bool {
 	return true
 }
 
-// Exists tests whether the set contains any value for which a function applied
-// to the value returns true. If the function does not return true for any value
-// in the set, Exists returns false. This is the logical inverse of Forall.
-func (s Of[T]) Exists(f func(T) bool) bool {
+// Find returns the first value for which a function applied to the value
+// returns true. If the function does not return true for any value
+// in the set, Find returns false and the zero value of T.
+//
+// if several set elements would match, the first match will be chosen
+// arbitrarily because the iteration order is indeterminate.
+//
+// Find can also be used for two special cases:
+//   - To test whether any value exists that matches the predicate,
+//     a true boolean result is all that matters.
+//   - To test whether any value exists that does not match the predicate,
+//     in this case the inverse function should be supplied and
+//     a false result is all that matters.
+func (s Of[T]) Find(f func(T) bool) (T, bool) {
 	for val := range s {
 		if f(val) {
-			return true
+			return val, true
 		}
 	}
-	return false
-}
-
-// Forall tests whether a given function returns true when applied to all values
-// in the set. If so, Forall returns true, otherwise it returns false. This is the
-// logical inverse of Exists.
-func (s Of[T]) Forall(f func(T) bool) bool {
-	for val := range s {
-		if !f(val) {
-			return false
-		}
-	}
-	return true
+	var zero T
+	return zero, false
 }
 
 // Each calls a function on each element of the set in an indeterminate order.

set/set_test.go

@@ -24,24 +24,17 @@ func TestSet(t *testing.T) {
 		t.Errorf("got %v, want [1 2 3 4 5 6]", got)
 	}
 
-	exists1 := s.Exists(func(val int) bool { return val > 3 })
+	v1, exists1 := s.Find(func(val int) bool { return val > 3 })
 	if !exists1 {
-		t.Errorf("Exists(val > 3) failed")
+		t.Errorf("Find(val > 3) failed")
 	}
-
-	exists2 := s.Exists(func(val int) bool { return val > 10 })
-	if exists2 {
-		t.Errorf("Exists(val > 103) failed")
+	if v1 <= 3 {
+		t.Errorf("Find(val > 3) failed with %d", v1)
 	}
 
-	forall1 := s.Forall(func(val int) bool { return val >= 1 })
-	if !forall1 {
-		t.Errorf("Forall(val >= 1) failed")
-	}
-
-	forall2 := s.Forall(func(val int) bool { return val > 2 })
-	if forall2 {
-		t.Errorf("Forall(val > 2) failed")
+	_, exists2 := s.Find(func(val int) bool { return val > 10 })
+	if exists2 {
+		t.Errorf("Find(val > 10) failed")
 	}
 
 	s2 := New[int](5, 6, 7, 8)