Lazy-loading modules

Corvis has no lazy loading of modules: there is no loader that adds a module to the container after startup. The whole module graph is walked and instantiated in CorvisFactory::create, before the first request is served.

In other environments lazy loading exists mostly to reduce the cold start time of serverless functions, where loading code is expensive. In a Rust binary all the code is already compiled and linked, so the remaining cost is that of building the providers.

Alternatives

• Build on demand. If a provider is expensive to create and only used sometimes, don't register it as a singleton: mark it transient and resolve it with module_ref.resolve::<T>().await, or build it when needed with module_ref.create::<T>().await. See Module reference.
• Deferred initialization inside the provider. A tokio::sync::OnceCell field (with #[default]) lets you create the expensive resource the first time it is used, keeping a single registered provider.
• Choosing modules at compile time. Cargo features and #[cfg(feature = "...")] let you include or exclude entire modules from the binary.
• Separate contexts. CorvisFactory::create_application_context::<AnotherModule>() creates an independent container (without an HTTP server) from another root module, for example for a one-off task. See Standalone applications.