From: Konrad Rosenbaum <konrad@silmor.de>
Date: Thu, 29 Dec 2011 09:44:26 +0000 (+0100)
Subject: some fixes for Nullable, add an explicit null value
X-Git-Url: http://git.silmor.de/gitweb/?a=commitdiff_plain;h=6a565edd00675310f956428a83791b8ba3f16a7b;p=web%2Fkonrad%2Fpack.git

some fixes for Nullable, add an explicit null value
---

diff --git a/qtbase/include/nullable.h b/qtbase/include/nullable.h
index 94fe369..c447f2f 100644
--- a/qtbase/include/nullable.h
+++ b/qtbase/include/nullable.h
@@ -7,16 +7,38 @@
 #ifndef WOLF_NULLABLE_H
 #define WOLF_NULLABLE_H
 
+///special class for Null values
+class NullValue
+{
+	public: 
+		NullValue(){} 
+		NullValue(const NullValue&){}
+		
+// 		operator void*()const{return (void*)0;}
+		template<typename T> operator T*()const{return (T*)0;}
+		
+		bool operator==(const NullValue&)const{return true;}
+		bool operator!=(const NullValue&)const{return false;}
+		
+		template<typename T>bool operator==(const T*p)const{return p==0;}
+		template<typename T>bool operator!=(const T*p)const{return p!=0;}
+};
+
+///special null value
+const NullValue nullval;
+
 /**wrapper around scalar values that makes them NULL-able, i.e. the virtual value NULL is added to the range of the wrapped value; wrapped classes must have a default constructor and =, == and != operators*/
 template<class T>class Nullable
 {
 	public:
 		/**creates a NULL value*/
-		Nullable(){isnull=true;elem=T();}
+		Nullable():isnull(true),elem(){}
+		/**creates a NULL value*/
+		Nullable(const NullValue&):isnull(true),elem(){}
 		/**creates a wrapped non-NULL value that is equivalent to the original*/
-		Nullable(const T&t){isnull=false;elem=t;}
+		Nullable(const T&t):isnull(false),elem(t){}
 		/**copies a nullable value*/
-		Nullable(const Nullable<T>&t){isnull=t.isnull;elem=t.elem;}
+		Nullable(const Nullable<T>&t):isnull(t.isnull),elem(t.elem){}
 		
 		/**makes this instance non-NULL and equivalent to the given value*/
 		Nullable<T>& operator=(const T&t){isnull=false;elem=t;return *this;}
@@ -49,6 +71,11 @@ template<class T>class Nullable
 			if(isnull != t.isnull)return true;
 			if(isnull)return false;
 			else return elem != t.elem;}
+		
+		///compares the Nullable with the special null value
+		bool operator==(const NullValue&)const{return isnull;}
+		///compares the Nullable with the special null value
+		bool operator!=(const NullValue&)const{return !isnull;}
 	private:
 		bool isnull;
 		T elem;
@@ -57,6 +84,7 @@ template<class T>class Nullable
 #include<QString>
 #include<QMetaType>
 //convenience wrappers
+Q_DECLARE_METATYPE(NullValue);
 Q_DECLARE_METATYPE(Nullable<bool>)
 Q_DECLARE_METATYPE(Nullable<qint32>)
 Q_DECLARE_METATYPE(Nullable<qint64>)