Added SelectArg and MemFunSelectArg*

The MemFunSelectArg* functions can be used to select
a specific argument from a signal. For example this would
select the string argument as argument to the callback:

Signal<void, int, float, string> signal;
signal.connect(MemFunSelectArg2(obj, &Object::takesOneStringArg));
signal.emit(10, 3.14, "hello");

...

void Object::takesOneStringArg(const string& value) {
...
}

src/FbTk/MemFun.hh

@@ -22,6 +22,8 @@
 #ifndef FBTK_MEM_FUN_HH
 #define FBTK_MEM_FUN_HH
 
+#include "SelectArg.hh"
+
 namespace FbTk {
 
 /// No argument functor
@@ -218,6 +220,60 @@ MemFunIgnoreArgs( Object& obj, ReturnType (Object:: *action)(Arg1,Arg2) ) {
     return MemFun2IgnoreArgs<ReturnType, Object, Arg1, Arg2>(obj, action);
 }
 
+/**
+ * Creates a functor that selects a specific argument of three possible ones
+ * and uses it for the single argument operator.
+ */
+template < int ArgNum, typename Functor>
+class MemFunSelectArgImpl {
+public:
+
+    MemFunSelectArgImpl(Functor func):
+        m_func(func) {
+    }
+
+    template <typename Type1, typename Type2, typename Type3>
+    void operator ()(Type1 a, Type2 b, Type3 c) {
+        m_func(STLUtil::SelectArg<ArgNum>()(a, b, c));
+    }
+
+    template <typename Type1, typename Type2>
+    void operator ()(Type1 a, Type2 b) {
+        m_func(STLUtil::SelectArg<ArgNum>()(a, b));
+    }
+
+    template <typename Type1>
+    void operator ()(Type1 a) {
+        m_func(a);
+    }
+
+private:
+    Functor m_func;
+};
+
+/// Creates a functor that selects the first argument of three possible ones
+/// and uses it for the single argument operator.
+template <typename ReturnType, typename Object, typename Arg1>
+MemFunSelectArgImpl<0, MemFun1<ReturnType, Object, Arg1> >
+MemFunSelectArg0(Object& obj, ReturnType (Object:: *action)(Arg1)) {
+    return MemFunSelectArgImpl<0, MemFun1<ReturnType, Object, Arg1> >(MemFun(obj, action));
+}
+
+/// Creates a functor that selects the second argument (or first if there is
+/// only one) of three possible onesand uses it for the single argument operator.
+template <typename ReturnType, typename Object, typename Arg1>
+MemFunSelectArgImpl<1, MemFun1<ReturnType, Object, Arg1> >
+MemFunSelectArg1(Object& obj, ReturnType (Object:: *action)(Arg1)) {
+    return MemFunSelectArgImpl<1, MemFun1<ReturnType, Object, Arg1> >(MemFun(obj, action));
+}
+
+/// Creates a functor that selects the third argument (or the last argument if there is
+/// less than three arguments) of three possible onesand uses it for the single argument operator.
+template <typename ReturnType, typename Object, typename Arg1>
+MemFunSelectArgImpl<2, MemFun1<ReturnType, Object, Arg1> >
+MemFunSelectArg2(Object& obj, ReturnType (Object:: *action)(Arg1)) {
+    return MemFunSelectArgImpl<2, MemFun1<ReturnType, Object, Arg1> >(MemFun(obj, action));
+}
 
 } // namespace FbTk
 

src/FbTk/STLUtil.hh

@@ -26,6 +26,25 @@
 namespace FbTk {
 namespace STLUtil {
 
+template<bool C, typename Ta, typename Tb>
+struct IfThenElse;
+
+template<typename Ta, typename Tb>
+struct IfThenElse<true, Ta, Tb> {
+    Ta& operator ()(Ta& ta, Tb& tb) const {
+        return ta;
+    }
+    typedef Ta ResultType;
+};
+
+template<typename Ta, typename Tb>
+struct IfThenElse<false, Ta, Tb> {
+    Tb& operator ()(Ta& ta, Tb& tb) const {
+        return tb;
+    }
+    typedef Tb ResultType;
+};
+
 /// calls delete on each item in the container and then clears the container
 template <typename A>
 void destroyAndClear(A &a) {

src/FbTk/SelectArg.hh

@@ -0,0 +1,74 @@
+// SelectArg.hh for FbTk
+// Copyright (c) 2010 Fluxbox Team (fluxgen at fluxbox dot org)
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+#ifndef FBTK_STLUTIL_SELECT_ARG_HH
+#define FBTK_STLUTIL_SELECT_ARG_HH
+
+#include "STLUtil.hh"
+
+namespace FbTk {
+
+namespace STLUtil {
+
+/**
+ * Selects a single argument from a maximum set of three arguments at compile time.
+ * For example:
+ * \begincode
+ * SelectArg<0>()( 10, 20, "hello" ); // returns first argument ( 10 )
+ * SelectArg<1>()( 10, "hello", 30 ); // returns second argument ( "hello" )
+ * SelectArg<2>()( 10, "hello", 30 ); // returns third argument ( 30 )
+ * \endcode
+ *
+ * The selection of argument 1 and 2 can return the last argument if the
+ * arguments are less or equal to two. For instance:
+ * \begincode
+ * SelectArg<1>()(10); // returns 10
+ * SelectArg<2>()(10, 20); // returns 20
+ * SelectArg<2>()(10); // returns 10
+ * \endcode
+ */
+template < int N >
+struct SelectArg {
+
+    template <typename Type1, typename Type2>
+    typename IfThenElse<N==0, Type1, Type2>::ResultType& operator ()(Type1& a, Type2& b){
+        return IfThenElse<N==0, Type1, Type2>()(a, b);
+    }
+
+    template <typename Type1, typename Type2, typename Type3>
+    typename IfThenElse<N==0, Type1,
+                        typename IfThenElse<N==1, Type2, Type3>::ResultType>::ResultType&
+     operator () (Type1& a, Type2& b, Type3& c) {
+        return IfThenElse<N==0, Type1,
+            typename IfThenElse<N==1, Type2, Type3>::ResultType>()
+            (a, IfThenElse<N==1, Type2, Type3>() (b, c) );
+    }
+
+    template < typename Type1 >
+    Type1 operator() (Type1 a) {
+        return a;
+    }
+};
+
+} // end namespace STLUtil
+} // end namespace FbTk
+
+#endif // FBTK_STLUTIL_SELECT_ARG_HH

src/tests/testSignals.cc

@@ -49,7 +49,7 @@ struct FunctionClass {
     }
 
     void takeIt( string& str ) {
-        cout << "takeIt( " << str << ")" << endl;
+        cout << "FunctionClass::takeIt( " << str << " )" << endl;
     }
 
     void showMessage( int value, const string& message ) {
@@ -61,8 +61,21 @@ struct FunctionClass {
     void threeArgs( int value, const string& str, double pi ) {
         cout << "(" << value << "): " << str << ", pi = " << pi << endl;
     }
+
 };
 
+struct Printer {
+    void printInt(int value) {
+        cout << "Int:" << value << endl;
+    }
+    void printString(string value) {
+        cout << "string:" << value << endl;
+    }
+    void printFloat(float value) {
+        cout << "Float:" << value << endl;
+    }
+}; 
+
 int main() {
     using FbTk::Signal;
     using FbTk::SignalTracker;
@@ -161,4 +174,22 @@ int main() {
         // subject notify its observers
         source.emit("hello world");
     }
+
+    // Test argument selector
+    {
+        using namespace FbTk;
+        Signal<void, int, string, float> source;
+
+        Printer printer;
+        source.connect(MemFunSelectArg0(printer, &Printer::printInt));
+        source.connect(MemFunSelectArg1(printer, &Printer::printString));
+        source.connect(MemFunSelectArg2(printer, &Printer::printFloat));
+
+        source.emit(10, "hello", 3.141592);
+
+        Signal<void, string, int> source2;
+        source2.connect(MemFunSelectArg0(printer, &Printer::printString));
+        source2.connect(MemFunSelectArg1(printer, &Printer::printInt));
+        source2.emit("world", 37);
+    }
 }