redi - Registry pattern meets Dependency Injection

Overview

redi is a dependency injection library focusing on providing a great developer experience.

#include <cstdio>
#include <optional>

import redi;

struct WindowSystem {};

struct RenderSystem {
    explicit RenderSystem(std::optional<WindowSystem&> window_system)
        : window_system{ window_system }
    {}

    std::optional<WindowSystem&> window_system;
};

template <>
struct redi::EntryTraits<RenderSystem> {
    static void describe_build(redi::BuildDirector<RenderSystem>& build_director)
    {
        build_director.use_dependencies<std::optional<WindowSystem&>>();
    }
};

int main()
{
    /*
     * Registering `RenderSystem` automatically registers `WindowSystem`
     * as well when it is an unconditional dependency.
     */
    redi::Registry registry = redi::RegistryBuilder{}
                                  .register_entry<RenderSystem>()
                                  // order doesn't matter
                                  .register_entry<WindowSystem>()
                                  .build();
    
    /*
     * `RenderSystem` is never headless when `WindowSystem` is present
     */
    std::puts(
        registry.at<RenderSystem>().window_system.has_value()
            ? "Renderer is not headless"
            : "Renderer is headless"
    );
}

Key Features

• Automatic dependency injection
  • Dependencies are automatically registered. You only need to register the concrete types you use.
• Optional dependencies
  • Feel free to describe all the optional dependencies your types may need. They will be delivered when they are present.
• Support for configurable builder objects
  • Use the builder method for complex building patterns.
• Elegant error messages

  Cyclic dependency detected - entry of type `WindowSystem` depends on itself (WindowSystem -> RenderSystem -> WindowSystem)
  

• Optimized for compile times
  • redi intentionally bypasses compile-time dependency detection. By eliminating the need to track transitive dependencies per source file, it significantly speeds up compilation.

Tutorial

Read the tutorial for an in-depth guide on how to inject dependencies using the library.

Installation

The library has no dependencies. You can include it as a subdirectory, use FetchContent, or use Conan.

Read more about the specific Conan workflow here.