Merge pull request #777 from elbeno/msg-indexing

🚸 Add `operator[]` to messages

Author: elbeno

include/msg/message.hpp

@@ -198,7 +198,10 @@ template <stdx::ct_string Name, typename... Fields> class msg_access {
     using FieldsTuple =
         decltype(stdx::make_indexed_tuple<name_for>(Fields{}...));
 
-    template <typename Field, stdx::range R> constexpr static auto check() {
+    template <typename N, stdx::range R> constexpr static auto check() {
+        static_assert((std::is_same_v<N, name_for<Fields>> or ...),
+                      "Field does not belong to this message!");
+        using Field = field_t<N>;
         constexpr auto belongs = (std::is_same_v<typename Field::field_id,
                                                  typename Fields::field_id> or
                                   ...);
@@ -209,20 +212,20 @@ template <stdx::ct_string Name, typename... Fields> class msg_access {
 
     template <stdx::range R, some_field_value V>
     constexpr static auto set1(R &&r, V v) -> void {
+        check<name_for<V>, std::remove_cvref_t<R>>();
         using Field = field_t<name_for<V>>;
-        check<Field, std::remove_cvref_t<R>>();
         Field::insert(std::forward<R>(r),
                       static_cast<typename Field::value_type>(v.value));
     }
 
     template <typename N, stdx::range R>
     constexpr static auto set_default(R &&r) -> void {
-        check<field_t<N>, std::remove_cvref_t<R>>();
+        check<N, std::remove_cvref_t<R>>();
         field_t<N>::insert_default(std::forward<R>(r));
     }
 
     template <typename N, stdx::range R> constexpr static auto get(R &&r) {
-        check<field_t<N>, std::remove_cvref_t<R>>();
+        check<N, std::remove_cvref_t<R>>();
         return field_t<N>::extract(std::forward<R>(r));
     }
 
@@ -341,11 +344,36 @@ template <stdx::ct_string Name, typename Access, typename T> struct msg_base {
     [[nodiscard]] constexpr auto get(auto f) const {
         return Access::get(as_derived().data(), f);
     }
+
     constexpr auto set(auto... fs) -> void {
         Access::set(as_derived().data(), fs...);
     }
     constexpr auto set() -> void {}
 
+    template <stdx::ct_string N> struct proxy {
+        // NOLINTNEXTLINE(cppcoreguidelines-avoid-const-or-ref-data-members)
+        msg_base &b;
+
+        // NOLINTNEXTLINE(misc-unconventional-assign-operator)
+        constexpr auto operator=(auto val) const && -> void {
+            b.set(field_name<N>{} = val);
+        }
+
+        using V = decltype(b.get(std::declval<field_name<N>>()));
+
+        // NOLINTNEXTLINE(google-explicit-constructor)
+        constexpr operator V() const { return b.get(field_name<N>{}); }
+    };
+
+    template <stdx::ct_string N>
+    [[nodiscard]] constexpr auto operator[](field_name<N> f) const {
+        return get(f);
+    }
+    template <stdx::ct_string N>
+    [[nodiscard]] constexpr auto operator[](field_name<N>) LIFETIMEBOUND {
+        return proxy<N>{*this};
+    }
+
     [[nodiscard]] constexpr auto describe() const {
         return Access::describe(as_derived().data());
     }

test/msg/fail/CMakeLists.txt

@@ -13,8 +13,12 @@ add_compile_fail_test(message_cmp_view.cpp LIBRARIES warnings cib_msg)
 add_compile_fail_test(message_const_field_write.cpp LIBRARIES warnings cib_msg)
 add_compile_fail_test(message_dangling_view.cpp LIBRARIES warnings cib_msg)
 add_compile_fail_test(message_dup_fieldnames.cpp LIBRARIES warnings cib_msg)
+add_compile_fail_test(message_get_nonexistent_field.cpp LIBRARIES warnings
+                      cib_msg)
 add_compile_fail_test(message_incompatible_matcher.cpp LIBRARIES warnings
                       cib_msg)
+add_compile_fail_test(message_set_nonexistent_field.cpp LIBRARIES warnings
+                      cib_msg)
 add_compile_fail_test(message_uninitialized_field.cpp LIBRARIES warnings
                       cib_msg)
 add_compile_fail_test(view_upsize.cpp LIBRARIES warnings cib_msg)

test/msg/fail/message_get_nonexistent_field.cpp

@@ -0,0 +1,17 @@
+#include <msg/field.hpp>
+#include <msg/message.hpp>
+
+// EXPECT: Field does not belong to this message
+namespace {
+using namespace msg;
+
+using test_field1 =
+    field<"test_field", std::uint32_t>::located<at{0_dw, 31_msb, 24_lsb}>;
+
+using msg_defn = message<"test_msg", test_field1>;
+} // namespace
+
+auto main() -> int {
+    owning<msg_defn> m{};
+    [[maybe_unused]] auto f = m.get("no"_field);
+}

test/msg/fail/message_set_nonexistent_field.cpp

@@ -0,0 +1,17 @@
+#include <msg/field.hpp>
+#include <msg/message.hpp>
+
+// EXPECT: Field does not belong to this message
+namespace {
+using namespace msg;
+
+using test_field1 =
+    field<"test_field", std::uint32_t>::located<at{0_dw, 31_msb, 24_lsb}>;
+
+using msg_defn = message<"test_msg", test_field1>;
+} // namespace
+
+auto main() -> int {
+    owning<msg_defn> m{};
+    m.set("no"_field = 1);
+}

test/msg/message.cpp

@@ -792,3 +792,18 @@ TEST_CASE("pack appends environments", "[message]") {
     using defn = pack<"defn", std::uint8_t, m1, m2>;
     STATIC_REQUIRE(custom(defn::env_t{}) == 18);
 }
+
+TEST_CASE("read indexing operator on message", "[message]") {
+    test_msg const msg{};
+    CHECK(0x80 == msg["id"_field]);
+}
+
+// This test causes clang-14 with libc++ to crash...
+#if not __clang__ or __clang_major__ > 14
+TEST_CASE("write indexing operator on message", "[message]") {
+    test_msg msg{};
+    CHECK((0 == msg["f1"_field]));
+    msg["f1"_field] = 0xba11;
+    CHECK((0xba11 == msg["f1"_field]));
+}
+#endif