Add make_visitor, make_accept_returning

1 files changed, 112 insertions, 0 deletions

diff --git a/paludis/util/visitor.hh b/paludis/util/visitor.hh
index 547e27231..8b2c0d96a 100644
--- a/paludis/util/visitor.hh
+++ b/paludis/util/visitor.hh
@@ -112,6 +112,112 @@ namespace paludis
         return AcceptVisitorReturning<Visitor_, Returning_>(v);
     }
 
+    template <typename>
+    struct ExtractFirstArgumentType;
+
+    template <typename T_, typename R_, typename A1_, typename... As_>
+    struct ExtractFirstArgumentType<R_ (T_::*) (A1_, As_...) const>
+    {
+        typedef A1_ Type;
+    };
+
+    template <typename T_>
+    using FirstCallArgumentType = typename ExtractFirstArgumentType<decltype(&T_::operator())>::Type;
+
+    template <typename>
+    struct ExtractResultType;
+
+    template <typename T_, typename R_, typename... As_>
+    struct ExtractResultType<R_ (T_::*) (As_...) const>
+    {
+        typedef R_ Type;
+    };
+
+    template <typename T_>
+    using CallResultType = typename ExtractResultType<decltype(&T_::operator())>::Type;
+
+    template <typename Revisitor_, typename Result_, typename... Cases_>
+    struct MadeVisitor;
+
+    template <typename Revisitor_, typename Result_>
+    struct MadeVisitor<Revisitor_, Result_>
+    {
+        Result_ visit(const NoType<0u> &) const;
+    };
+
+    template <typename>
+    struct CallThisCaseNeedsTwoArgs;
+
+    template <typename T_, typename R_, typename A1_>
+    struct CallThisCaseNeedsTwoArgs<R_ (T_::*) (A1_) const>
+    {
+        enum { value = false };
+    };
+
+    template <typename T_, typename R_, typename A1_, typename A2_>
+    struct CallThisCaseNeedsTwoArgs<R_ (T_::*) (A1_, A2_) const>
+    {
+        enum { value = true };
+    };
+
+    template <typename Result_, typename Case_, typename V_, bool needs_two_args_>
+    struct CallThisCase;
+
+    template <typename Result_, typename Case_, typename V_>
+    struct CallThisCase<Result_, Case_, V_, false>
+    {
+        static Result_ call(const Case_ & thiscase, const FirstCallArgumentType<Case_> & v, const V_ &)
+        {
+            return thiscase(v);
+        }
+    };
+
+    template <typename Result_, typename Case_, typename V_>
+    struct CallThisCase<Result_, Case_, V_, true>
+    {
+        static Result_ call(const Case_ & thiscase, const FirstCallArgumentType<Case_> & v, const V_ & revisitor)
+        {
+            return thiscase(v, accept_visitor_returning<Result_>(revisitor));
+        }
+    };
+
+    template <typename Revisitor_, typename Result_, typename Case_, typename... Rest_>
+    struct MadeVisitor<Revisitor_, Result_, Case_, Rest_...> :
+        MadeVisitor<Revisitor_, Result_, Rest_...>
+    {
+        const Case_ & thiscase;
+
+        MadeVisitor(const Case_ & c, const Rest_ & ... cases) :
+            MadeVisitor<Revisitor_, Result_, Rest_...>(cases...),
+            thiscase(c)
+        {
+        }
+
+        using MadeVisitor<Revisitor_, Result_, Rest_...>::visit;
+
+        Result_ visit(const FirstCallArgumentType<Case_> & v) const
+        {
+            return CallThisCase<Result_, Case_, Revisitor_, CallThisCaseNeedsTwoArgs<decltype(&Case_::operator())>::value>::call(
+                    thiscase, v, *static_cast<const Revisitor_ *>(this));
+        }
+    };
+
+    template <typename Result_, typename... Cases_>
+    struct BaseMadeVisitor :
+        MadeVisitor<BaseMadeVisitor<Result_, Cases_...>, Result_, Cases_...>
+    {
+        BaseMadeVisitor(const Cases_ & ... cases) :
+            MadeVisitor<BaseMadeVisitor<Result_, Cases_...>, Result_, Cases_...>(cases...)
+        {
+        }
+    };
+
+    template <typename Case_, typename... Cases_>
+    auto make_visitor(const Case_ & firstcase, const Cases_ & ... cases) -> BaseMadeVisitor<CallResultType<Case_>, Case_, Cases_...>
+    {
+        return BaseMadeVisitor<CallResultType<Case_>, Case_, Cases_...>{ firstcase, cases... };
+    }
+
     template <>
     class DeclareAbstractVisitMethods<TypeListTail>
     {
@@ -274,6 +380,12 @@ namespace paludis
                 _real_accept_const(vv);
                 return vv.result;
             }
+
+            template <typename Case_, typename... Cases_>
+            auto make_accept_returning(const Case_ & firstcase, const Cases_ & ... cases) const -> CallResultType<Case_>
+            {
+                return this->accept_returning<CallResultType<Case_> >(make_visitor(firstcase, cases...));
+            }
     };
 
     template <typename BaseClass_, typename RealClass_>