dependencyinjection

dependencyinjection

A simple dependency injection library using Golang generics

Usage

The library has two main concepts, Container and Provider.

A Container is the object that stores all the dependencies, a global container is provided dependencyinjection.Global.

A Provider provides a dependency, there are currently three implemented Provided types, Singleton, Factory and Value:

• Singleton - Constructor will only be called once, result is used for all subsequent dependency resolutions.
• Factory - Constructor is run every time the dependency is resolved.
• Value - The static provided value is returned when the dependency is resolved.

Custom Provider types can be used also, by implementing the Provider interface. This could allow for more complex strategies.

Example

In this simple example a type Config is added to the global container. This an then later be resolved by objects that require it using dependencyinjection.Get[Config](ctx, dependencyinjection.Global).

func init() {
    // Register Config into the dependency injection container, in this example it loads the config from the filesystem.
    dependencyinjection.MustRegisterSingleton(dependencyinjection.Global, func(ctx context.Context, container *dependencyinjection.Container) (Config, error) {
        // Get filesystem, this allows different implementations to be provided. In reality for config files the real
        // filesystem will be the one used 99% of the time, but this illustrates how to get dependencies.
        //
        // An example of how the fs.FS object could have been added to the container is as follows:
        //  dependencyinjection.MustRegisterValue(dependencyinjection.Global, os.DirFS("/some/path"))
        //
        filesystem, err := dependencyinjection.Get[fs.FS](ctx, container)
        if err != nil {
            return Config{}, err
        }

        // Load the config
        file, err := filesystem.Open("config.json")
        if err != nil {
            return Config{}, err
        }

        // Ensure file gets closed
        defer file.Close()

        // Parse the config from a file
        var config Config
        if err := json.NewDecoder(file).Decode(&config); err != nil {
            return Config{}, err
        }

        // Return loaded config
        return config, nil
    })
}