ReferencePtr.h

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#ifndef SimTK_SimTKCOMMON_REFERENCE_PTR_H_
#define SimTK_SimTKCOMMON_REFERENCE_PTR_H_

/* -------------------------------------------------------------------------- *
 *                       Simbody(tm): SimTKcommon                             *
 * -------------------------------------------------------------------------- *
 * This is part of the SimTK biosimulation toolkit originating from           *
 * Simbios, the NIH National Center for Physics-Based Simulation of           *
 * Biological Structures at Stanford, funded under the NIH Roadmap for        *
 * Medical Research, grant U54 GM072970. See https://simtk.org/home/simbody.  *
 *                                                                            *
 * Portions copyright (c) 2012 Stanford University and the Authors.           *
 * Authors: Michael Sherman                                                   *
 * Contributors:                                                              *
 *                                                                            *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may    *
 * not use this file except in compliance with the License. You may obtain a  *
 * copy of the License at http://www.apache.org/licenses/LICENSE-2.0.         *
 *                                                                            *
 * Unless required by applicable law or agreed to in writing, software        *
 * distributed under the License is distributed on an "AS IS" BASIS,          *
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   *
 * See the License for the specific language governing permissions and        *
 * limitations under the License.                                             *
 * -------------------------------------------------------------------------- */

namespace SimTK {

template <class T> class ReferencePtr {
public:
    typedef T  element_type;
    typedef T* pointer;
    typedef T& reference;

    ReferencePtr() : p(0) { }
    explicit ReferencePtr(T* tp) : p(tp) { }
    explicit ReferencePtr(T& t) : p(&t) { }
    ReferencePtr(const ReferencePtr&) : p(0) { }
    ReferencePtr& operator=(const ReferencePtr& r) 
    {   if (&r != this) clear(); return *this; }
    ReferencePtr& operator=(T& t)          
    {  reset(&t); return *this; }
    ReferencePtr& operator=(T* tp)               
    {   reset(tp); return *this; }
    
    ~ReferencePtr() {clear();} // just being tidy

    T* operator->() const { return &getRef(); }

    T& operator*() const { return getRef(); }

    operator T*() const { return p; }

    operator bool() const { return !empty(); }

    T* get()  const  { return p; }

    T& getRef() const { 
        SimTK_ERRCHK(p!=0, "ReferencePtr::getRef()", 
                    "An attempt was made to dereference a null pointer."); 
        return *p; 
    }

    bool     empty() const    { return p==0; }
    void     clear()          { p=0; }
    T*       release()        { T* x=p; p=0; return x; }
    void     reset(T* tp)     { p=tp;}

    void swap(ReferencePtr& other) {
        T* otherp = other.release();
        other.reset(p);
        reset(otherp);
    }
     
private:
    // Warning: ReferencePtr must be exactly the same size as type T*. That way
    // one can reinterpret_cast a T* to a ReferencePtr<T> when needed.
    T*    p;  
};    
    
} // namespace SimTK

namespace std {
template <class T> inline void
swap(SimTK::ReferencePtr<T>& p1, SimTK::ReferencePtr<T>& p2) {
    p1.swap(p2);
}

} // namespace std

#endif // SimTK_SimTKCOMMON_REFERENCE_PTR_H_