Make rfl::num_fields public (#465)

Author: bryceschober

docs/custom_parser.md

@@ -1,9 +1,10 @@
 # Custom parsers
 
-## `rfl::Reflector` 
+## `rfl::Reflector`
 
-If you absolutely do not want to make any changes to your original classes whatsoever,
-You can create a Reflector template specialization for your type:
+If you absolutely do not want to (or are unable to) make any changes to your
+original classes whatsoever, you can create a Reflector template specialization
+for your type:
 
 ```cpp
 namespace rfl {
@@ -13,7 +14,7 @@ struct Reflector<Person> {
     std::string first_name;
     std::string last_name;
   };
-  
+
   static Person to(const ReflType& v) noexcept {
     return {v.first_name, v.last_name};
   }
@@ -25,7 +26,27 @@ struct Reflector<Person> {
 }
 ```
 
-It's also fine to define just the `from` method when the original class is 
+One way to help make sure that your `ReflType` is kept up to date with your
+original class is to use the `rfl::num_fields<T>` utility to implement a compile-
+time assertion to verify that they have the same number of fields. The
+`rfl::num_fields<T>` utility can be used even in cases where the original
+class is too complex for `reflect-cpp`'s default reflection logic or
+`rfl::to_view()` to be able to handle.
+
+```cpp
+namespace rfl {
+template <>
+struct Reflector<Person> {
+  struct ReflType {
+    std::string first_name;
+    std::string last_name;
+  };
+  static_assert(rfl::num_fields<ReflType> == rfl::num_fields<Person>,
+    "ReflType and actual type must have the same number of fields");
+  // ...
+```
+
+It's also fine to define just the `from` method when the original class is
 only written, or `to` when the original class is only read:
 
 ```cpp
@@ -46,7 +67,7 @@ struct Reflector<Person> {
 ```
 
 Note that the `ReflType` does not have to be a struct. For instance, if you have
-a custom type called `MyCustomType` that you want to be serialized as a string, 
+a custom type called `MyCustomType` that you want to be serialized as a string,
 you can do the following:
 
 ```cpp
@@ -114,7 +135,7 @@ struct Person {
 };
 ```
 
-You can then write a helper struct: 
+You can then write a helper struct:
 
 ```cpp
 struct PersonImpl {

docs/docs-readme.md

@@ -28,11 +28,11 @@
 
 [Standard containers](standard_containers.md) - Describes how reflect-cpp treats containers in the standard library.
 
-[C arrays and inheritance](c_arrays_and_inheritance.md) - Describes how reflect-cpp handles C arrays and inheritance. 
+[C arrays and inheritance](c_arrays_and_inheritance.md) - Describes how reflect-cpp handles C arrays and inheritance.
 
-[rfl::Bytestring](bytestring.md) - Describes how reflect-cpp handles binary strings for formats that support them. 
+[rfl::Bytestring](bytestring.md) - Describes how reflect-cpp handles binary strings for formats that support them.
 
-[rfl::Binary, rfl::Hex and rfl::Oct](number_systems.md)- For expressing numbers in different formats. 
+[rfl::Binary, rfl::Hex and rfl::Oct](number_systems.md)- For expressing numbers in different formats.
 
 ## Validation
 
@@ -58,7 +58,7 @@
 
 [Custom classes](concepts/custom_classes.md) - For custom classes with private fields.
 
-[Custom parsers for your classes](custom_parser.md) - For custom classes with private fields that you want to leave absolutely untouched.
+[Custom parsers for your classes](custom_parser.md) - For custom classes with private fields that you want (or need) to leave absolutely untouched.
 
 ## Useful helper functions and classes
 

include/rfl/num_fields.hpp

@@ -0,0 +1,14 @@
+#ifndef RFL_NUM_FIELDS_HPP_
+#define RFL_NUM_FIELDS_HPP_
+
+#include "internal/num_fields.hpp"
+
+namespace rfl {
+
+/// Returns the number of fields fields.
+template <class T>
+constexpr std::size_t num_fields = internal::num_fields<T>;
+
+}  // namespace rfl
+
+#endif

tests/README.md

@@ -3,8 +3,8 @@
 reflect-cpp uses vcpkg for dependency management, including
 gtest, which is required for the tests.
 
-```bash
-# bootstrap vcpkg if you haven't done so already 
+```shell
+# bootstrap vcpkg if you haven't done so already
 git submodule update --init
 ./vcpkg/bootstrap-vcpkg.sh # Linux, macOS
 ./vcpkg/bootstrap-vcpkg.bat # Windows
@@ -15,29 +15,35 @@ git submodule update --init
 
 To compile the tests, do the following:
 
-```bash
+```shell
 cmake -S . -B build -DCMAKE_CXX_STANDARD=20 -DCMAKE_BUILD_TYPE=Release -DREFLECTCPP_BUILD_TESTS=ON
 cmake --build build -j 4 # gcc, clang
 cmake --build build --config Release -j 4 # MSVC
 ```
 
 To run the tests, do the following:
 
-```
+```shell
 ./build/tests/json/reflect-cpp-json-tests
 ```
 
 ## All serialization formats
 
 To compile the tests with serialization formats other than JSON, do the following:
 
-```bash
+```shell
 cmake -S . -B build -DCMAKE_CXX_STANDARD=20 -DREFLECTCPP_BUILD_TESTS=ON -DREFLECTCPP_AVRO=ON -DREFLECTCPP_BSON=ON -DREFLECTCPP_CAPNPROTO=ON -DREFLECTCPP_CBOR=ON -DREFLECTCPP_FLEXBUFFERS=ON -DREFLECTCPP_MSGPACK=ON -DREFLECTCPP_XML=ON -DREFLECTCPP_TOML=ON -DREFLECTCPP_UBJSON=ON -DREFLECTCPP_YAML=ON -DCMAKE_BUILD_TYPE=Release
 cmake --build build -j 4 # gcc, clang
 cmake --build build --config Release -j 4 # MSVC
 ```
 
-To run the tests, do the following:
+You can run all of the tests via `ctest`, as in:
+
+```shell
+ctest --test-dir build --output-on-failure
+```
+
+Or you can run tests individually, as in:
 
 ```
 ./build/tests/avro/reflect-cpp-avro-tests

tests/json_c_arrays_and_inheritance/test_inheritance2.cpp

@@ -4,7 +4,7 @@
 #include <iostream>
 #include <rfl.hpp>
 
-#include "rfl/internal/num_fields.hpp"
+#include "rfl/num_fields.hpp"
 
 namespace test_inheritance2 {
 
@@ -31,23 +31,28 @@ struct EmptyDerived2 : EmptyBase1, EmptyBase2, BaseX {};
 TEST(json, test_inheritance2) {
   Derived1 derived1;
   const auto derived1_view = rfl::to_view(derived1);
+  static_assert(rfl::num_fields<Derived1> == 2);
   static_assert(derived1_view.size() == 2);
 
   Derived2 derived2;
   const auto derived2_view = rfl::to_view(derived2);
+  static_assert(rfl::num_fields<Derived2> == 3);
   static_assert(derived2_view.size() == 3);
 
-  EmptyDerived1 empty_derived0;
+  EmptyDerived0 empty_derived0;
   auto empty_derived0_view = rfl::to_view(empty_derived0);
+  static_assert(rfl::num_fields<EmptyDerived0> == 2);
   static_assert(empty_derived0_view.size() == 2);
 
   EmptyDerived1 empty_derived1;
   auto empty_derived1_view = rfl::to_view(empty_derived1);
+  static_assert(rfl::num_fields<EmptyDerived1> == 2);
   static_assert(empty_derived1_view.size() == 2);
 
-  EmptyDerived1 empty_derived2;
+  EmptyDerived2 empty_derived2;
   auto empty_derived2_view = rfl::to_view(empty_derived2);
-  static_assert(empty_derived0_view.size() == 2);
+  static_assert(rfl::num_fields<EmptyDerived1> == 2);
+  static_assert(empty_derived2_view.size() == 2);
 
   EXPECT_TRUE(true);
 }