replaced try blocks with scope guards

include/boost/unordered/detail/foa.hpp

@@ -1147,21 +1147,15 @@ public:
     }
     else{
       reserve(x.size());
-      BOOST_TRY{
+      clear_on_exit c{x};
-        /* This works because subsequent x.clear() does not depend on the
+      (void)c; /* unused var warning */
-         * elements' values.
-         */
 
-        x.for_all_elements([this](value_type* p){
+      /* This works because subsequent x.clear() does not depend on the
-          unchecked_insert(type_policy::move(*p));
+        * elements' values.
-        });
+        */
-      }
+      x.for_all_elements([this](value_type* p){
-      BOOST_CATCH(...){
+        unchecked_insert(type_policy::move(*p));
-        x.clear();
+      });
-        BOOST_RETHROW
-      }
-      BOOST_CATCH_END
-      x.clear();
     }
   }
 
@@ -1209,19 +1203,6 @@ public:
     static constexpr auto pocma=
       alloc_traits::propagate_on_container_move_assignment::value;
 
-    /* Avoid using nested lambdas with a `this` capture as it seems to trigger
-     * a bug in GCC:
-     * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80947
-     * 
-     * Rather than directly attempting to manipulate the visibility of the
-     * table class, it's easier to work around the bug by simply un-nesting the
-     * lambda.
-     */
-
-    auto const move_element=[this](value_type* p){
-      unchecked_insert(type_policy::move(*p));
-    };
-
     if(this!=std::addressof(x)){
       clear();
       h()=std::move(x.h());
@@ -1234,28 +1215,19 @@ public:
         swap(arrays,x.arrays);
         swap(ml,x.ml);
       }
-      else if_constexpr<!alloc_traits::is_always_equal::value>([&,this]{
+      else{
-        /* The check above is redundant: we're setting up a compile-time
-         * barrier so that the compiler is convinced we're not throwing
-         * under noexcept(true) conditions.
-         */
-
         /* noshrink: favor memory reuse over tightness */
         noshrink_reserve(x.size());
-        BOOST_TRY{
+        clear_on_exit c{x};
-          /* This works because subsequent x.clear() does not depend on the
+        (void)c; /* unused var warning */
-           * elements' values.
-           */
 
-          x.for_all_elements(move_element);
+        /* This works because subsequent x.clear() does not depend on the
-        }
+         * elements' values.
-        BOOST_CATCH(...){
+         */
-          x.clear();
+        x.for_all_elements([this](value_type* p){
-          BOOST_RETHROW
+          unchecked_insert(type_policy::move(*p));
-        }
+        });
-        BOOST_CATCH_END
+      }
-        x.clear();
-      });
     }
     return *this;
   }
@@ -1452,6 +1424,12 @@ private:
   template<typename,typename,typename,typename> friend class table;
   using arrays_type=table_arrays<value_type,group_type,size_policy>;
 
+  struct clear_on_exit
+  {
+    ~clear_on_exit(){x.clear();}
+    table& x;
+  };
+
   Hash&            h(){return hash_base::get();}
   const Hash&      h()const{return hash_base::get();}
   Pred&            pred(){return pred_base::get();}