From 1f2037ff984ee05944ed9b8f5d85adb3214cc2c4 Mon Sep 17 00:00:00 2001
From: Mingxin Wang <mingxwa@microsoft.com>
Date: Thu, 26 Dec 2024 19:32:16 +1000
Subject: [PATCH] Replace macro `PRO_DEF_WEAK_DISPATCH` with class template
 `weak_dispatch` (#224)

---
 proxy.h                                       | 55 +++++++++++++++----
 .../freestanding/proxy_freestanding_tests.cpp |  8 +--
 tests/proxy_invocation_tests.cpp              | 27 +++------
 3 files changed, 55 insertions(+), 35 deletions(-)

diff --git a/proxy.h b/proxy.h
index 6378f8e..1bb6ba9 100644
--- a/proxy.h
+++ b/proxy.h
@@ -6,8 +6,10 @@
 
 #include <cassert>
 #include <cstddef>
+#include <cstdlib>
 #include <bit>
 #include <concepts>
+#include <exception>
 #include <initializer_list>
 #include <limits>
 #include <memory>
@@ -16,9 +18,6 @@
 #include <utility>
 
 #ifdef __cpp_rtti
-#ifndef __cpp_exceptions
-#include <cstdlib>  // For std::abort() when "throw" is not available
-#endif  // __cpp_exceptions
 #include <optional>
 #include <typeinfo>
 #endif  // __cpp_rtti
@@ -31,6 +30,12 @@
 #error "Proxy requires C++20 attribute no_unique_address"
 #endif
 
+#ifdef __cpp_exceptions
+#define ___PRO_THROW(...) throw __VA_ARGS__
+#else
+#define ___PRO_THROW(...) std::abort()
+#endif  // __cpp_exceptions
+
 #ifdef _MSC_VER
 #define ___PRO_ENFORCE_EBO __declspec(empty_bases)
 #else
@@ -1256,7 +1261,11 @@ using proxy_view = proxy<observer_facade<F>>;
         accessor() noexcept { ::std::ignore = &accessor::__VA_ARGS__; })
 
 #ifdef __cpp_rtti
-struct bad_proxy_cast : std::bad_cast {};
+class bad_proxy_cast : public std::bad_cast {
+ public:
+  bad_proxy_cast() noexcept = default;
+  char const* what() const noexcept override { return "pro::bad_proxy_cast"; }
+};
 #endif  // __cpp_rtti
 
 namespace details {
@@ -1554,12 +1563,6 @@ template <std::size_t N>
 sign(const char (&str)[N]) -> sign<N>;
 
 #ifdef __cpp_rtti
-#ifdef __cpp_exceptions
-#define ___PRO_THROW(...) throw __VA_ARGS__
-#else
-#define ___PRO_THROW(...) std::abort()
-#endif  // __cpp_exceptions
-
 struct proxy_cast_context {
   const std::type_info* type_ptr;
   bool is_ref;
@@ -1657,9 +1660,21 @@ ___PRO_DEBUG(
 
   const std::type_info* info;
 };
-#undef ___PRO_THROW
 #endif  // __cpp_rtti
 
+struct wildcard {
+  wildcard() = delete;
+
+  template <class T>
+  [[noreturn]] operator T() {
+#ifdef __cpp_lib_unreachable
+    std::unreachable();
+#else
+    std::abort();
+#endif  // __cpp_lib_unreachable
+  }
+};
+
 }  // namespace details
 
 template <class Cs, class Rs, proxiable_ptr_constraints C>
@@ -1969,6 +1984,20 @@ struct explicit_conversion_dispatch : details::cast_dispatch_base<true, false> {
 };
 using conversion_dispatch = explicit_conversion_dispatch;
 
+class not_implemented : public std::exception {
+ public:
+  not_implemented() noexcept = default;
+  char const* what() const noexcept override { return "pro::not_implemented"; }
+};
+
+template <class D>
+struct weak_dispatch : D {
+  using D::operator();
+  template <class... Args>
+  [[noreturn]] details::wildcard operator()(std::nullptr_t, Args&&...)
+      { ___PRO_THROW(not_implemented{}); }
+};
+
 #define ___PRO_EXPAND_IMPL(__X) __X
 #define ___PRO_EXPAND_MACRO_IMPL( \
     __MACRO, __1, __2, __3, __NAME, ...) \
@@ -2049,7 +2078,8 @@ ___PRO_DEBUG( \
     ___PRO_EXPAND_MACRO(___PRO_DEF_FREE_AS_MEM_DISPATCH, __NAME, __VA_ARGS__)
 
 #define PRO_DEF_WEAK_DISPATCH(__NAME, __D, __FUNC) \
-    struct __NAME : __D { \
+    struct [[deprecated("'PRO_DEF_WEAK_DISPATCH' is deprecated. " \
+        "Use pro::weak_dispatch<" #__D "> instead.")]] __NAME : __D { \
       using __D::operator(); \
       template <class... __Args> \
       decltype(auto) operator()(::std::nullptr_t, __Args&&... __args) \
@@ -2058,6 +2088,7 @@ ___PRO_DEBUG( \
 
 }  // namespace pro
 
+#undef ___PRO_THROW
 #undef ___PRO_NO_UNIQUE_ADDRESS_ATTRIBUTE
 
 #endif  // _MSFT_PROXY_
diff --git a/tests/freestanding/proxy_freestanding_tests.cpp b/tests/freestanding/proxy_freestanding_tests.cpp
index 11eb8f9..fc584e5 100644
--- a/tests/freestanding/proxy_freestanding_tests.cpp
+++ b/tests/freestanding/proxy_freestanding_tests.cpp
@@ -4,6 +4,7 @@
 
 #include "proxy.h"
 
+constexpr unsigned DefaultHash = -1;
 unsigned GetHash(int v) { return static_cast<unsigned>(v + 3) * 31; }
 unsigned GetHash(double v) { return static_cast<unsigned>(v * v + 5) * 87; }
 unsigned GetHash(const char* v) {
@@ -13,12 +14,11 @@ unsigned GetHash(const char* v) {
   }
   return result;
 }
-unsigned GetDefaultHash() { return -1; }
+unsigned GetHash(std::nullptr_t) { return DefaultHash; }
 
 PRO_DEF_FREE_DISPATCH(FreeGetHash, GetHash);
-PRO_DEF_WEAK_DISPATCH(WeakFreeGetHash, FreeGetHash, GetDefaultHash);
 struct Hashable : pro::facade_builder
-    ::add_convention<WeakFreeGetHash, unsigned()>
+    ::add_convention<FreeGetHash, unsigned()>
     ::build {};
 
 extern "C" int main() {
@@ -40,7 +40,7 @@ extern "C" int main() {
     return 1;
   }
   p = &t;
-  if (GetHash(*p) != GetDefaultHash()) {
+  if (GetHash(*p) != DefaultHash) {
     return 1;
   }
   return 0;
diff --git a/tests/proxy_invocation_tests.cpp b/tests/proxy_invocation_tests.cpp
index bd059a7..c56fa73 100644
--- a/tests/proxy_invocation_tests.cpp
+++ b/tests/proxy_invocation_tests.cpp
@@ -36,18 +36,10 @@ struct Callable : pro::facade_builder
     ::add_facade<MovableCallable<Os...>>
     ::build {};
 
-struct Wildcard {
-  template <class T>
-  operator T() const noexcept { std::terminate(); }
-};
-
-Wildcard NotImplemented(auto&&...) { throw std::runtime_error{ "Not implemented!" }; }
-
-PRO_DEF_WEAK_DISPATCH(WeakOpCall, pro::operator_dispatch<"()">, NotImplemented);
 template <class... Os>
 struct WeakCallable : pro::facade_builder
     ::support_copy<pro::constraint_level::nontrivial>
-    ::add_convention<WeakOpCall, Os...>
+    ::add_convention<pro::weak_dispatch<pro::operator_dispatch<"()">>, Os...>
     ::build {};
 
 PRO_DEF_FREE_DISPATCH(FreeSize, std::ranges::size, Size);
@@ -77,10 +69,9 @@ struct Container : pro::facade_builder
     ::build {};
 
 PRO_DEF_MEM_DISPATCH(MemAt, at, at);
-PRO_DEF_WEAK_DISPATCH(MemAtWeak, MemAt, NotImplemented);
 
 struct ResourceDictionary : pro::facade_builder
-    ::add_convention<MemAtWeak, std::string(int)>
+    ::add_convention<pro::weak_dispatch<MemAt>, std::string(int)>
     ::build {};
 
 template <class F, class T>
@@ -101,12 +92,12 @@ struct Weak : pro::facade_builder
     ::build {};
 
 template <class F, class T>
-auto GetWeakImpl(const std::shared_ptr<T>& p) { return pro::make_proxy<Weak<F>, std::weak_ptr<T>>(p); }
-
+pro::proxy<Weak<F>> GetWeakImpl(const std::shared_ptr<T>& p) { return pro::make_proxy<Weak<F>, std::weak_ptr<T>>(p); }
 template <class F>
-PRO_DEF_FREE_DISPATCH(FreeGetWeakImpl, GetWeakImpl<F>, GetWeak);
+pro::proxy<Weak<F>> GetWeakImpl(std::nullptr_t) { return nullptr; }
+
 template <class F>
-PRO_DEF_WEAK_DISPATCH(FreeGetWeak, FreeGetWeakImpl<F>, std::nullptr_t);
+PRO_DEF_FREE_DISPATCH(FreeGetWeak, GetWeakImpl<F>, GetWeak);
 
 struct SharedStringable : pro::facade_builder
     ::add_facade<utils::spec::Stringable>
@@ -272,9 +263,8 @@ TEST(ProxyInvocationTests, TestMemberDispatchDefault) {
     bool exception_thrown = false;
     try {
       p->at(0);
-    } catch (const std::runtime_error& e) {
+    } catch (const pro::not_implemented&) {
       exception_thrown = true;
-      ASSERT_EQ(static_cast<std::string>(e.what()), "Not implemented!");
     }
     ASSERT_TRUE(exception_thrown);
   }
@@ -292,9 +282,8 @@ TEST(ProxyInvocationTests, TestFreeDispatchDefault) {
     auto p = pro::make_proxy<details::WeakCallable<void()>>(123);
     try {
       (*p)();
-    } catch (const std::runtime_error& e) {
+    } catch (const pro::not_implemented&) {
       exception_thrown = true;
-      ASSERT_EQ(static_cast<std::string>(e.what()), "Not implemented!");
     }
     ASSERT_TRUE(exception_thrown);
   }