Added toOptional function.

source/handy_http_primitives/optional.d

@@ -123,11 +123,11 @@ struct Optional(T) {
             * Params:
             *   serializer = The serializer to use (provided by ASDF).
             */
-            void serialize(S)(ref S serializer) {
+            void serialize(S)(ref S serializer) const {
                 if (this.isNull) {
                     serializer.putValue(null);
                 } else {
-                    serializer.putValue(this.value);
+                    serializeValue(serializer, this.value);
                 }
             }
         }
@@ -147,6 +147,18 @@ auto mapIfPresent(alias fn, T)(Optional!T opt) {
     return Optional!U.of(fn(opt.value));
 }
 
+/**
+ * Helper function to get an Optional value for an existing value. Due to D's
+ * type inference, you can simply write `auto opt = toOptional(x);` to avoid
+ * having to write out types when constructing optionals.
+ * Params:
+ *   t = The value to construct an optional from.
+ * Returns: The optional with the given value.
+ */
+Optional!T toOptional(T)(T t) {
+    return Optional!T.of(t);
+}
+
 unittest {
     Optional!string s = Optional!string.of("hello");
     assert(!s.isNull);
@@ -196,7 +208,7 @@ unittest {
             immutable int x;
         }
         Optional!Invalid opt = Optional!(Invalid).of(Invalid(42));
-        static assert(!__traits(compiles, serializeToJson(opt)));
+        static assert(__traits(compiles, serializeToJson(opt)));
         try {
             deserialize!(Optional!(Invalid))(`{"x": 123}`);
             assert(
@@ -208,3 +220,11 @@ unittest {
         }
     }
 }
+
+// Tests for toOptional.
+unittest {
+    int x = 5;
+    auto optX = x.toOptional;
+    assert(!optX.isNull);
+    assert(optX.value == 5);
+}