parse/enum: return a cookie we could use for cleanup on setup

CMakeLists.txt

@@ -409,6 +409,7 @@ list (
     parallel/queue.hpp
     parallel/stack.cpp
     parallel/stack.hpp
+    parse/fwd.hpp
     parse/enum.cpp
     parse/enum.hpp
     parse/time.cpp

parse/enum.hpp

@@ -8,6 +8,8 @@
 
 #pragma once
 
+#include "fwd.hpp"
+
 #include "../view.hpp"
 #include "../introspection.hpp"
 #include "../log.hpp"
@@ -90,7 +92,7 @@ namespace cruft::parse::enumeration {
 
 
     template <typename EnumT>
-    void setup (std::map<std::string_view, EnumT> mapping)
+    cookie setup [[nodiscard]] (std::map<std::string_view, EnumT> mapping)
     {
         auto &cache = detail::cache ();
 
@@ -100,7 +102,9 @@ namespace cruft::parse::enumeration {
         auto [pos, success] = cache.insert ({ index, std::move (lookup) });
         if (!success)
             LOG_WARN ("duplicate parse setup for %! was ignored", cruft::type_name<EnumT> ());
-    }
+
+        return cookie {};
+    };
 
 
     template <typename EnumT>

parse/fwd.hpp

@@ -0,0 +1,15 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * Copyright 2019, Danny Robson <danny@nerdcruft.net>
+ */
+
+#pragma once
+
+namespace cruft::parse {
+    namespace enumeration {
+        struct cookie {};
+    }
+}

test/parse/enum.cpp

@@ -7,11 +7,12 @@ enum enumeration_t : u16 { FOO, BAR = 2, QUX = 257 };
 
 int main ()
 {
-    cruft::parse::enumeration::setup<enumeration_t> ({
+    auto const cookie = cruft::parse::enumeration::setup<enumeration_t> ({
         { "FOO", FOO },
         { "BAR", BAR },
         { "QUX", QUX },
     });
+    (void)cookie;
 
     cruft::TAP::logger tap;
     tap.expect_eq (FOO, cruft::parse::from_string<enumeration_t> ("FOO"), "enumeration, FOO");