From 1e0abc3a49ade6a4fa1b38f744df070c40a87724 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 1 Dec 2012 22:58:19 +0200
Subject: [PATCH] Store the value of the key in key_error

The type of the container is uninformative and often ugly.
---
 source/core/maputils.cpp |  8 +++++---
 source/core/maputils.h   | 44 +++++++++++++++++++++++++++++++++++-----
 2 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/source/core/maputils.cpp b/source/core/maputils.cpp
index 4fcc8e2..28739f0 100644
--- a/source/core/maputils.cpp
+++ b/source/core/maputils.cpp
@@ -1,12 +1,14 @@
 #include <msp/debug/demangle.h>
+#include <msp/strings/format.h>
 #include "maputils.h"
 
 using namespace std;
 
 namespace Msp {
 
-key_error::key_error(const type_info &t):
-	runtime_error(Debug::demangle(t.name()))
-{ }
+string key_error::make_what(const type_info &type, const string &value)
+{
+	return format("%s(%s)", Debug::demangle(type.name()), value);
+}
 
 } // namespace Msp
diff --git a/source/core/maputils.h b/source/core/maputils.h
index 9548714..8c642fb 100644
--- a/source/core/maputils.h
+++ b/source/core/maputils.h
@@ -3,14 +3,48 @@
 
 #include <stdexcept>
 #include <typeinfo>
+#include <msp/strings/lexicalcast.h>
 
 namespace Msp {
 
+namespace MapUtilsInternal {
+
+/* This must be hidden in the internal namespace to avoid interfering with
+other things.  There may be problems if a key type has operator<< for ostream
+but not LexicalConverter. */
+template<typename T>
+void operator<<(LexicalConverter &, const T &)
+{ }
+
+template<typename T>
+static std::string stringify_key(const T &k)
+{
+	try
+	{
+		LexicalConverter conv((Fmt()));
+		conv<<k;
+		return conv.get();
+	}
+	catch(const lexical_error &)
+	{
+		return "<cannot display value>";
+	}
+}
+
+} // namespace Internal
+
 class key_error: public std::runtime_error
 {
 public:
-	key_error(const std::type_info &);
-	~key_error() throw() { }
+	template<typename T>
+	key_error(const T &k):
+		runtime_error(make_what(typeid(T), MapUtilsInternal::stringify_key(k)))
+	{ }
+
+	virtual ~key_error() throw() { }
+
+private:
+	static std::string make_what(const std::type_info &, const std::string &);
 };
 
 
@@ -19,7 +53,7 @@ typename T::mapped_type &get_item(T &map, const typename T::key_type &key)
 {
 	typename T::iterator i = map.find(key);
 	if(i==map.end())
-		throw key_error(typeid(T));
+		throw key_error(key);
 
 	return i->second;
 }
@@ -29,7 +63,7 @@ const typename T::mapped_type &get_item(const T &map, const typename T::key_type
 {
 	typename T::const_iterator i = map.find(key);
 	if(i==map.end())
-		throw key_error(typeid(T));
+		throw key_error(key);
 
 	return i->second;
 }
@@ -38,7 +72,7 @@ template<typename T>
 const typename T::iterator insert_unique(T &map, const typename T::key_type &key, const typename T::mapped_type &item)
 {
 	if(map.count(key))
-		throw key_error(typeid(T));
+		throw key_error(key);
 
 	return map.insert(typename T::value_type(key, item)).first;
 }
-- 
2.45.2