[shared_ptr]

test initialization from nullptr
fix bool cast of Dune implementation

[[Imported from SVN: r7040]]

dune/common/shared_ptr.hh

@@ -112,6 +112,11 @@ namespace Dune
       return rep_==0 ? 0 : rep_->rep_;
     }
 
+    /** \brief Checks if shared_ptr manages an object, i.e. whether get() != 0. */
+    explicit operator bool() const {
+      return rep_ != 0 && rep_->rep_ != 0;
+    }
+
     /** \brief Swap content of this shared_ptr and another */
     inline void swap(shared_ptr& other);
 

dune/common/test/shared_ptrtest.cc

@@ -128,6 +128,11 @@ int main(){
     shared_ptr<double> bar(new double(43.0));
     assert(bar);
 
+    // test constructor from nullptr
+    shared_ptr<double> bar_null(nullptr);
+    assert(!bar_null);
+    assert(!bar_null.get());
+
     // test reset()
     bar.reset();
     assert(!bar);