Merge pull request #59 from grandseiken/main

add rfl::NamedTuple::apply() for convenient compile-time iteration

Author: liuzicheng1987

README.md

@@ -281,7 +281,7 @@ for (const auto& f : rfl::fields<Person>()) {
 }
 ```
 
-You can also create a view and then access these fields using `std::get` or `rfl::get`:
+You can also create a view and then access these fields using `std::get` or `rfl::get`, or iterate over the fields at compile-time:
 
 ```cpp
 auto lisa = Person{.first_name = "Lisa", .last_name = "Simpson", .age = 8};
@@ -298,6 +298,11 @@ const auto view = rfl::to_view(lisa);
 *view.get<"age">() = 0;
 *rfl::get<0>(view) = "Maggie";
 *rfl::get<"first_name">(view) = "Maggie";
+
+view.apply([](const auto& f) {
+  // f is a an rfl::Field pointing to the original field.
+  std::cout << f.name() << ": " << rfl::json::write(*f.value()) << std::endl;
+});
 ```
 
 It also possible to replace fields:

docs/named_tuple.md

@@ -95,6 +95,25 @@ const auto first_name = person.template get<"firstName">();
 const auto first_name = rfl::get<"firstName">(person);
 ```
 
+Fields can also be iterated over at compile-time using the `apply()` method:
+
+```cpp
+auto person = rfl::Field<"first_name", std::string>("Bart") *
+              rfl::Field<"last_name", std::string>("Simpson");
+
+person.apply([](const auto& f) {
+  auto field_name = f.name();
+  const auto& value = *f.value();
+});
+
+person.apply([]<typename Field>(Field& f) {
+  // The field name can also be obtained as a compile-time constant.
+  constexpr auto field_name = Field::name();
+  using field_pointer_type = typename Field::Type;
+  field_pointer_type* value = f.value();
+});
+```
+
 ### `rfl::replace`
 
 `rfl::replace` works for `rfl::NamedTuple` as well:

include/rfl/Field.hpp

@@ -62,6 +62,9 @@ struct Field {
   /// The name of the field, for internal use.
   constexpr static const internal::StringLiteral name_ = _name;
 
+  /// The name of the field.
+  constexpr static std::string_view name() { return name_.string_view(); }
+
   /// Returns the underlying object.
   const Type& get() const { return value_; }
 

include/rfl/NamedTuple.hpp

@@ -210,6 +210,26 @@ class NamedTuple {
     return rfl::make_field<_field_name>(rfl::get<_field_name>(*this));
   }
 
+  /// Invokes a callable object once for each field in order.
+  template <typename F>
+  void apply(F&& f) {
+    std::apply(
+        [&f]<typename... AFields>(AFields&&... fields) {
+          ((f(std::forward<AFields>(fields))), ...);
+        },
+        fields());
+  }
+
+  /// Invokes a callable object once for each field in order.
+  template <typename F>
+  void apply(F&& f) const {
+    std::apply(
+        [&f]<typename... AFields>(AFields&&... fields) {
+          ((f(std::forward<AFields>(fields))), ...);
+        },
+        fields());
+  }
+
   /// Copy assignment operator.
   NamedTuple<FieldTypes...>& operator=(
       const NamedTuple<FieldTypes...>& _other) = default;

tests/json/test_view.cpp

@@ -4,6 +4,7 @@
 #include <rfl/json.hpp>
 #include <source_location>
 #include <string>
+#include <type_traits>
 #include <vector>
 
 #include "test_replace.hpp"
@@ -30,5 +31,23 @@ void test() {
 
   write_and_read(lisa,
                  R"({"first_name":"Maggie","last_name":"Simpson","age":0})");
+
+  view.apply([]<typename Field>(const Field& field) {
+    using field_type = std::remove_pointer_t<typename Field::Type>;
+    if constexpr (Field::name() == "age") {
+      static_assert(std::is_same_v<field_type, int>);
+    } else {
+      static_assert(std::is_same_v<field_type, std::string>);
+    }
+  });
+
+  rfl::to_view(lisa).apply([](auto field) {
+    if constexpr (decltype(field)::name() == "first_name") {
+      *field.value() = "Bart";
+    }
+  });
+
+  write_and_read(lisa,
+                 R"({"first_name":"Bart","last_name":"Simpson","age":0})");
 }
 }  // namespace test_view