X-Git-Url: http://git.tdb.fi/?p=libs%2Fdatafile.git;a=blobdiff_plain;f=source%2Fobjectloader.h;h=a2a8720e840e6393f3e185950741fc6ba0df5729;hp=bab1ce5378f5bce344fd931d80061b6a67af9698;hb=07d4c0e55aa9571c9f24cf39d134f1f7474fd7cb;hpb=7df5e45c7f414f6a07681dc4ec2abb63b091a309

diff --git a/source/objectloader.h b/source/objectloader.h
index bab1ce5..a2a8720 100644
--- a/source/objectloader.h
+++ b/source/objectloader.h
@@ -1,11 +1,18 @@
 #ifndef MSP_DATAFILE_OBJECTLOADER_H_
 #define MSP_DATAFILE_OBJECTLOADER_H_
 
+#include <typeinfo>
 #include "loader.h"
 
 namespace Msp {
 namespace DataFile {
 
+class no_collection: public std::runtime_error
+{
+public:
+	no_collection(const std::type_info &);
+};
+
 class Collection;
 
 /**
@@ -28,6 +35,29 @@ public:
 };
 
 
+/**
+Convenience class for loading derived objects.  Inherits from the base class
+loader and shadows its members with ones for the derived type.
+*/
+template<typename O, typename B>
+class DerivedObjectLoader: public B
+{
+public:
+	typedef O Object;
+
+protected:
+	O &obj;
+
+	DerivedObjectLoader(O &o): B(o), obj(o) { }
+
+	template<typename T>
+	DerivedObjectLoader(O &o, T &a): B(o, a), obj(o) { }
+
+public:
+	O &get_object() const { return obj; }
+};
+
+
 /**
 Provides functionality for loading objects with a Collection.  Deriving from
 this allows loading pointers to objects in the collection automatically.
@@ -47,7 +77,7 @@ public:
 	C &get_collection() const
 	{
 		if(!coll)
-			throw InvalidState("No collection");
+			throw no_collection(typeid(O));
 		return *coll;
 	}
 };