[injection] Create an example implementation

Author: Yaraslaut

example/inject/CMakeLists.txt

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+add_executable(injector injection_impl.cpp)
+target_link_libraries(injector PRIVATE rsl-inject)

example/inject/injection_impl.cpp

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+#include "interface.hpp"
+#include <rsl/inject>
+
+
+namespace foo_impl
+{
+  static constexpr auto target_name = "injected_implementation";
+  [[=Inject("demo/file.cpp")]]
+  std::string generateFunction()
+  {
+    return " int foo() { return 42;}";
+  }
+} // namespace inject
+
+
+RSLINJECT_ENABLE_NS(foo_impl)

example/inject/interface.hpp

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+#pragma once
+
+int foo();

example/inject/main.cpp

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+#include <print>
+#include "interface.hpp"
+
+auto main(int argc, char *argv[]) -> int {
+  std::println("{}", foo());
+  return 0;
+}

include/rsl/inject

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+#include <meta>
+#include <string>
+#include <fstream>
+#include <filesystem>
+#include <format>
+#include <unordered_map>
+#include <set>
+
+#include <rsl/span>
+
+namespace __impl{
+
+struct InjectPath {
+  char const* msg;
+
+};
+} // namespace __impl
+
+
+static consteval auto Inject(char const* msg) {
+    return __impl::InjectPath{std::define_static_string(msg)};
+};
+
+
+using injections_type = std::unordered_map<std::filesystem::path, std::string>;
+
+struct injection_info
+{
+  injections_type entries;
+  std::string target_name;
+};
+
+injection_info& injection_info() {
+  static struct injection_info injected{};
+  return injected;
+}
+
+injections_type& injections(){
+  return injection_info().entries;
+}
+
+std::string generate_cmake() {
+  std::string out{};
+  auto& info = injection_info();
+  // boilerplate
+
+  return out;
+}
+
+template<std::meta::info func>
+void process_injection()
+{
+  constexpr auto vec = rsl::span{std::define_static_array(std::meta::annotations_of(func))};
+  constexpr std::string_view annotationInfo = std::define_static_string(std::meta::extract<__impl::InjectPath>(vec[0]).msg);
+  auto const path = std::filesystem::path(annotationInfo);
+  std::format_to(std::back_inserter(injections()[path]), "{}\n", [:func:]() );
+}
+
+void generate_from_injection()
+{
+  for(const auto [path,injection] : injections())
+    {
+      if(path.has_parent_path())
+        std::filesystem::create_directories(path.parent_path());
+      std::ofstream file{path};
+      if(file)
+        file << injection;
+    }
+}
+
+template<std::meta::info source>
+constexpr bool gather_injections() {
+  template for (constexpr auto member : define_static_array(members_of(source, std::meta::access_context::current()))) {
+    if constexpr(is_function(member))
+      process_injection<member>();
+  }
+  return true;
+}
+
+#define RSLINJECT_ENABLE_NS(NS)                                                 \
+  namespace {                                                                 \
+  [[maybe_unused]] static bool const _rsl_injection_enabled = \
+      gather_injections<^^NS>();               \
+  }
+
+int main()
+{
+  generate_from_injection();
+}