Add ValueOrDefault to optional type (#30)

opt/value.go

@@ -10,6 +10,15 @@ type T[D any] struct {
 	Value D
 }
 
+// ValueOrDefault returns the value held in this optional if it is specified,
+// otherwise it returns the given fallback value.
+func (t T[D]) ValueOrDefault(fallback D) D {
+	if t.Specified {
+		return t.Value
+	}
+	return fallback
+}
+
 // ToPtr returns a pointer-based representation of the value held
 // in this optional. If this optional is not specified, then nil
 // is returned.

opt/value_test.go

@@ -32,6 +32,13 @@ var _ = Describe("Optional", func() {
 		Expect(v.Value).To(Equal(actual))
 	})
 
+	It("is possible to get a fallback value", func() {
+		v := opt.Unspecified[string]()
+		Expect(v.ValueOrDefault("fallback")).To(Equal("fallback"))
+		v = opt.V("hello")
+		Expect(v.ValueOrDefault("fallback")).To(Equal("hello"))
+	})
+
 	It("is possible to get a pointer representation of an unspecified value", func() {
 		v := opt.Unspecified[string]()
 		ptr := v.ToPtr()