Added a document about the coding conventions used in GiNaC. Corrections,

[ginac.git] / ginac / ptr.h

diff --git a/ginac/ptr.h b/ginac/ptr.h
index fd380506fdd6daaec5183e94f8557c7306f51f4c..93b16416f5471d9bd9eb165fd7d159767a3f2522 100644 (file)
--- a/ginac/ptr.h
+++ b/ginac/ptr.h
@@ -23,6 +23,7 @@
 #ifndef __GINAC_PTR_H__
 #define __GINAC_PTR_H__
 
+#include <cstddef> // for size_t
 #include <functional>
 #include <iosfwd>
 
@@ -30,12 +31,28 @@
 
 namespace GiNaC {
 
+
+/** Base class for reference-counted objects. */
+class refcounted {
+public:
+       refcounted() throw() : refcount(0) {}
+
+       size_t add_reference() throw() { return ++refcount; }
+       size_t remove_reference() throw() { return --refcount; }
+       size_t get_refcount() const throw() { return refcount; }
+       void set_refcount(size_t r) throw() { refcount = r; }
+
+private:
+       size_t refcount; ///< reference counter
+};
+
+
 /** Class of (intrusively) reference-counted pointers that support
  *  copy-on-write semantics.
  *
  *  Requirements for T:
- *    T::refcount member that supports ++refcount, --refcount, refcount = 1,
- *      refcount == 0 and refcount > 1
+ *    must support the refcounted interface (usually by being derived
+ *      from refcounted)
  *    T* T::duplicate() member function (only if makewriteable() is used) */
 template <class T> class ptr {
        friend class std::less< ptr<T> >;
@@ -48,24 +65,24 @@ public:
     // no default ctor: a ptr is never unbound
 
        /** Bind ptr to newly created object, start reference counting. */
-       ptr(T *t) throw() : p(t) { GINAC_ASSERT(p); p->refcount = 1; }
+       ptr(T *t) throw() : p(t) { GINAC_ASSERT(p); p->set_refcount(1); }
 
        /** Bind ptr to existing reference-counted object. */
-       explicit ptr(T &t) throw() : p(&t) { ++p->refcount; }
+       explicit ptr(T &t) throw() : p(&t) { p->add_reference(); }
 
-       ptr(const ptr & other) throw() : p(other.p) { ++p->refcount; }
+       ptr(const ptr & other) throw() : p(other.p) { p->add_reference(); }
 
        ~ptr()
        {
-               if (--p->refcount == 0)
+               if (p->remove_reference() == 0)
                        delete p;
        }
 
        ptr &operator=(const ptr & other)
        {
-               // NB: must first increment other.p->refcount, since other might be *this.
-               ++other.p->refcount;
-               if (--p->refcount == 0)
+               // NB: must first add reference to "other", since other might be *this.
+               other.p->add_reference();
+               if (p->remove_reference() == 0)
                        delete p;
                p = other.p;
                return *this;
@@ -80,10 +97,10 @@ public:
         *  This ensures that the object is not shared by any other ptrs. */
        void makewritable()
        {
-               if (p->refcount > 1) {
+               if (p->get_refcount() > 1) {
                        T *p2 = p->duplicate();
-                       p2->refcount = 1;
-                       --p->refcount;
+                       p2->set_refcount(1);
+                       p->remove_reference();
                        p = p2;
                }
        }
@@ -130,6 +147,7 @@ private:
 
 } // namespace GiNaC
 
+
 namespace std {
 
 /** Specialization of std::less for ptr<T> to enable ordering of ptr<T>