From ab956fd92f2110197c8e035b12dafa30a18b8ae1 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 25 May 2011 23:32:24 +0300
Subject: [PATCH] Improve error reporting in Variant

---
 source/core/variant.cpp | 13 +++++++++++++
 source/core/variant.h   | 19 ++++++++++++++++---
 2 files changed, 29 insertions(+), 3 deletions(-)
 create mode 100644 source/core/variant.cpp

diff --git a/source/core/variant.cpp b/source/core/variant.cpp
new file mode 100644
index 0000000..1cdc0a5
--- /dev/null
+++ b/source/core/variant.cpp
@@ -0,0 +1,13 @@
+#include <msp/debug/demangle.h>
+#include <msp/strings/formatter.h>
+#include "variant.h"
+
+using namespace std;
+
+namespace Msp {
+
+type_mismatch::type_mismatch(const type_info &e, const type_info &a):
+	runtime_error(format("expected: %s\nactual: %s", Debug::demangle(e.name()), Debug::demangle(a.name())))
+{ }
+
+}
diff --git a/source/core/variant.h b/source/core/variant.h
index 8d6db9a..f2d2ee5 100644
--- a/source/core/variant.h
+++ b/source/core/variant.h
@@ -8,18 +8,29 @@ Distributed under the LGPL
 #ifndef MSP_CORE_VARIANT_H_
 #define MSP_CORE_VARIANT_H_
 
-#include "except.h"
+#include <stdexcept>
+#include <typeinfo>
 #include "meta.h"
 
 namespace Msp {
 
+class type_mismatch: public std::runtime_error
+{
+public:
+	type_mismatch(const std::type_info &, const std::type_info &);
+	~type_mismatch() throw() { }
+};
+
+
 class Variant
 {
 private:
 	struct StoreBase
 	{
 		virtual ~StoreBase() { }
-		virtual StoreBase *clone() const =0;
+
+		virtual const std::type_info &type_id() const = 0;
+		virtual StoreBase *clone() const = 0;
 	};
 
 	template<typename T>
@@ -28,6 +39,8 @@ private:
 		T data;
 
 		Store(T d): data(d) { }
+
+		virtual const std::type_info &type_id() const { return typeid(T); }
 		virtual StoreBase *clone() const { return new Store<T>(data); }
 	};
 
@@ -61,7 +74,7 @@ public:
 		typedef typename RemoveConst<T>::Type NCT;
 		Store<NCT> *s = dynamic_cast<Store<NCT> *>(store);
 		if(!s)
-			throw InvalidState("Type mismatch");
+			throw type_mismatch(typeid(T), (store ? store->type_id() : typeid(void)));
 		return s->data;
 	}
 
-- 
2.45.2