typeidx: add lightweight runtime type id call

CMakeLists.txt

@@ -391,6 +391,8 @@ list (
     time.ipp
     tuple.cpp
     tuple.hpp
+    typeidx.cpp
+    typeidx.hpp
     types/bits.hpp
     types/comparator.hpp
     types/comparator.ipp
@@ -496,6 +498,7 @@ if (TESTS)
         stringid
         strongdef
         tuple
+        typeidx
         uri
         vector
         version

test/typeidx.cpp

@@ -0,0 +1,17 @@
+#include "tap.hpp"
+
+#include "./typeidx.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////
+int
+main (int, char**)
+{
+    util::TAP::logger tap;
+
+    tap.expect_eq (util::typeidx<int> (), util::typeidx<int> (), "equality for int");
+    tap.expect_eq (util::typeidx<float> (), util::typeidx<float> (), "equality for float");
+    tap.expect_neq (util::typeidx<int> (), util::typeidx<float> (), "inequality for int/float");
+
+    return tap.status ();
+}

typeidx.cpp

@@ -0,0 +1,26 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2017 Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "./typeidx.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////
+std::uintptr_t
+util::detail::typeidx_next ()
+{
+    static std::uintptr_t counter = 0;
+    return counter++;
+}

typeidx.hpp

@@ -0,0 +1,46 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2017 Danny Robson <danny@nerdcruft.net>
+ */
+
+#ifndef CRUFT_UTIL_TYPEIDX_HPP
+#define CRUFT_UTIL_TYPEIDX_HPP
+
+#include <cstdint>
+
+namespace util {
+    namespace detail { std::uintptr_t typeidx_next (void); }
+
+    /// return a globally unique runtime ID for a given type.
+    ///
+    /// this is intended to be used as a lightweight type check for variants
+    /// and such without requiring RTTI.
+    ///
+    /// the identifier is constructed at runtime and is not guaranteed to be
+    /// stable across executions (particularly in the case of threads and
+    /// other non-determinism).
+    ///
+    /// the range of identifiers is _probably_ contiguous starting from zero.
+    /// this should not be relied upon for correctness, but may be used for
+    /// performance concerns.
+    template <typename T>
+    std::uintptr_t
+    typeidx (void)
+    {
+        static auto id = detail::typeidx_next ();
+        return id;
+    }
+}
+
+#endif