%implicitconv will now accept None where the implicit conversion takes a C/C++ pointer.

Problem highlighted by Bo Peng on the swig-user mailing list. SF patch #230.

CHANGES.current

@@ -8,6 +8,10 @@ Version 2.0.11 (in progress)
 2013-08-23: olly
 	    [Python] Fix clang++ warning in generated wrapper code.
 
+2013-08-16: wsfulton
+            [Python] %implicitconv will now accept None where the implicit conversion takes a C/C++ pointer.
+            Problem highlighted by Bo Peng. Closes SF patch #230.
+
 2013-08-07: wsfulton
             [Python] SF Patch #326 from Kris Thielemans - Remove SwigPyObject_print and SwigPyObject_str and
             make the generated wrapper use the default python implementations, which will fall back to repr

Examples/test-suite/implicittest.i

@@ -46,7 +46,6 @@
     Foo(double){ ii = 2;}
     explicit Foo(char *s){ii = 3;}
     Foo(const Foo& f){ ii = f.ii;}
-    
   };
 
   struct Bar 
@@ -57,11 +56,31 @@
     Bar(const Foo& ff){ ii = ff.ii;}
   };
 
-
   int get_b(const Bar&b) { return b.ii; }
   
   Foo foo;
-  
 }
 
 %template(A_int) A_T<int>;
+
+
+/****************** None handling *********************/
+
+%inline
+{
+  struct BB {};
+  struct AA
+  {
+    int ii;
+    AA(int i) { ii = 1; }
+    AA(double d) { ii = 2; }
+    AA(const B* b) { ii = 3; }
+    explicit AA(char *s) { ii = 4; }
+    AA(const BB& b) { ii = 5; }
+
+    int get() const { return ii; }
+  };
+
+  int get_AA_val(AA a) { return a.ii; }
+  int get_AA_ref(const AA& a) { return a.ii; }
+}

Examples/test-suite/python/implicittest_runme.py

@@ -11,6 +11,14 @@ check(1, A(1).get())
 check(2, A(1.0).get())
 check(3, A(B()).get())
 check(4, A("hello").get())
+try:
+    check(3, A(None).get())
+    raise RuntimeError
+except ValueError:
+    # ValueError: invalid null reference in method 'new_A', argument 1 of type 'B const &'
+    # Arguably A(char *) should be chosen, but there is a bug to do with None passed to methods overloaded by value,
+    # references and pointers to different types, where pointers ought to be given a slightly higher precedence.
+    pass
 
 check(1, get(1))
 check(2, get(1.0))
@@ -71,3 +79,38 @@ try:
 except TypeError:
     pass
 
+#### Class testing None ####
+
+# No implicit conversion
+check(1, AA(1).get())
+check(2, AA(1.0).get())
+check(3, AA(B()).get())
+check(3, AA(None).get())
+check(4, AA("hello").get())
+check(5, AA(BB()).get())
+
+check(1, get_AA_val(1))
+check(2, get_AA_val(1.0))
+check(3, get_AA_val(B()))
+check(3, get_AA_val(None))
+check(5, get_AA_val(BB()))
+
+# Explicit constructor:
+try:
+    check(4, get_AA_val("hello"))
+    raise RuntimeError
+except TypeError:
+    pass
+
+check(1, get_AA_ref(1))
+check(2, get_AA_ref(1.0))
+check(3, get_AA_ref(B()))
+check(3, get_AA_ref(None))
+check(5, get_AA_ref(BB()))
+
+# Explicit constructor:
+try:
+    check(4, get_AA_ref("hello"))
+    raise RuntimeError
+except TypeError:
+    pass

Lib/python/pyrun.swg

@@ -1128,10 +1128,11 @@ SWIGRUNTIME int
 SWIG_Python_ConvertPtrAndOwn(PyObject *obj, void **ptr, swig_type_info *ty, int flags, int *own) {
   int res;
   SwigPyObject *sobj;
+  int implicit_conv = (flags & SWIG_POINTER_IMPLICIT_CONV) != 0;
 
   if (!obj)
     return SWIG_ERROR;
-  if (obj == Py_None) {
+  if (obj == Py_None && !implicit_conv) {
     if (ptr)
       *ptr = 0;
     return SWIG_OK;
@@ -1180,7 +1181,7 @@ SWIG_Python_ConvertPtrAndOwn(PyObject *obj, void **ptr, swig_type_info *ty, int
     }
     res = SWIG_OK;
   } else {
-    if (flags & SWIG_POINTER_IMPLICIT_CONV) {
+    if (implicit_conv) {
       SwigPyClientData *data = ty ? (SwigPyClientData *) ty->clientdata : 0;
       if (data && !data->implicitconv) {
         PyObject *klass = data->klass;
@@ -1215,6 +1216,13 @@ SWIG_Python_ConvertPtrAndOwn(PyObject *obj, void **ptr, swig_type_info *ty, int
         }
       }
     }
+    if (!SWIG_IsOK(res) && obj == Py_None) {
+      if (ptr)
+        *ptr = 0;
+      if (PyErr_Occurred())
+        PyErr_Clear();
+      res = SWIG_OK;
+    }
   }
   return res;
 }