+ // implicit conversion to "bool"
+
+#if defined(__SUNPRO_CC) && BOOST_WORKAROUND(__SUNPRO_CC, <= 0x530)
+
+ operator bool () const
+ {
+ return ptr != 0;
+ }
+
+#elif defined(__MWERKS__) && BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3003))
+ typedef T * (this_type::*unspecified_bool_type)() const;
+
+ operator unspecified_bool_type() const // never throws
+ {
+ return ptr == 0? 0: &this_type::get;
+ }
+
+#else
+
+ typedef T * this_type::*unspecified_bool_type;
+
+ operator unspecified_bool_type() const // never throws
+ {
+ return ptr == 0? 0: &this_type::ptr;
+ }
+
+#endif
+
+ bool operator! () const // never throws
+ {
+ return ptr == 0;
+ }
+