springtime_di/

component.rs

//! One of the basic blocks of dependency injection is a [Component]. Components are injectable
//! objects, which themselves can contain dependencies to other components.
//!
//! ## Registering concrete components
//!
//! Any type that wants to be managed by the DI system needs to implement `Component`. For
//! convenience, the trait can be automatically derived with all infrastructures if the `derive`
//! feature is enabled:
//!
//! ```
//! use springtime_di::component::Component;
//! use springtime_di::instance_provider::ComponentInstancePtr;
//! use springtime_di::{Component, component_alias, injectable};
//!
//! #[injectable]
//! trait TestTrait {}
//!
//! #[derive(Component)]
//! struct TestDependency;
//!
//! #[component_alias]
//! impl TestTrait for TestDependency {}
//!
//! #[derive(Component)]
//! #[component(names = ["dep2"])]
//! struct TestComponent {
//!     // concrete type dependency
//!     dependency_1: ComponentInstancePtr<TestDependency>,
//!     // primary dyn Trait dependency - note Send + Sync when using the "threadsafe" feature
//!     dependency_2: ComponentInstancePtr<dyn TestTrait + Send + Sync>,
//!     // optional dependency - don't fail when not present
//!     optional_dependency: Option<ComponentInstancePtr<TestDependency>>,
//!     // all registered dependencies of a given type
//!     all_dependencies: Vec<ComponentInstancePtr<dyn TestTrait + Sync + Send>>,
//!     #[component(default)]
//!     default: i8,
//!     #[component(default = "dummy_expr")]
//!     default_expr: i8,
//! }
//!
//! fn dummy_expr() -> i8 {
//!     -1
//! }
//! ```
//!
//! Please see the examples for more usage information.
//!
//! ### Supported `#[component]` struct configuration
//!
//! * `names = ["name"]` - use given name list as the component names, instead of the auto-generated
//!   one
//! * `condition = "expr"` - call `expr()` and evaluate if given component should be registered; see
//!   [crate::component_registry::conditional]
//! * `priority = number` - if a condition is present, use the given numerical priority to establish
//!   the order of registration in relation to other components with a condition (i8; higher is first;
//!   default is 0)
//! * `constructor = "expr"` - call `expr(dependencies...)` to construct the component, instead of
//!   using standard struct construction; parameters must be in the same order as fields in the struct
//!   while non-injected fields can be ignored with the `#[component(ignore)]` attribute
//! * `constructor_parameters = "params"` - additional injectable parameters for the above
//!   constructor; the "params" string consists of comma separated definitions in format:
//!   `(Type | Type/name | Option<Type> | Option<Type>/name | Vec<Type>)`, which means (in order):
//!   primary instance of `Type`, `name`d instance of `Type`, optional primary instance of `Type`,
//!   optional `name`d instance of `Type`, all instances of `Type`
//! * `scope = "name"` - use the [scope](crate::scope) named `name` or
//!   [SINGLETON](crate::scope::SINGLETON) as default
//!
//! ### Supported `#[component]` field configuration
//!
//! * `default` - use `Default::default()` initialization
//! * `default = "expr"` - call `expr()` for initialization
//! * `name = "name"` - inject instance named as `name`
//! * `ignore` - ignore the field when using custom constructor
//!
//! ## Registering component aliases
//!
//! Component aliases are different types, which can refer to a concrete component type. Usually
//! they are simply `dyn Traits`, which makes it possible to inject an abstract `dyn Trait` type
//! instead of a concrete component type. Each injectable trait should be marked as such, which can
//! be done with the `#[injectable]` helper attribute.
//!
//! To automatically register a component alias, use the `#[component_alias]` attribute on a trait
//! implementation:
//!
//! ```
//! use springtime_di::{Component, component_alias, injectable};
//!
//! #[derive(Component)]
//! struct SomeComponent;
//!
//! #[injectable]
//! trait SomeTrait {
//! }
//!
//! #[component_alias]
//! impl SomeTrait for SomeComponent {
//! }
//! ```
//!
//! The above example shows how it's possible to inject both `ComponentInstancePtr<SomeComponent>`
//! and `ComponentInstancePtr<dyn SomeTrait>`.
//!
//! ### Supported `#[component_alias]` arguments
//!
//! * `primary` - mark the concrete component, for which we're implementing the trait, as selected
//!   (primary) when requesting a single instance of `ComponentInstancePtr<dyn Trait>` and multiple
//!   components are available
//! * `condition = "expr"` - call `expr()` and evaluate if given component should be registered; see
//!   [crate::component_registry::conditional]
//! * `priority = number` - if a condition is present, use the given numerical priority to establish
//!   the order of registration in relation to other components with a condition (i8; higher
//!   is first; default is 0)
//! * `scope = "name"` - use the [scope](crate::scope) named `name` to override the concrete
//!   component scope

#[cfg(feature = "async")]
use crate::future::BoxFuture;
use crate::instance_provider::ComponentInstanceProviderError;
use crate::instance_provider::{
    ComponentInstanceAnyPtr, ComponentInstanceProvider, ComponentInstancePtr,
};

/// Base trait for components for dependency injection.
///
/// Components might depend on other components, which form the basis for dependency injection. To
/// make the system work, your component instances must be wrapped in a [ComponentInstancePtr].
/// Please see the module-level documentation for more information.
pub trait Component: ComponentDowncast<Self> + Sized {
    #[cfg(not(feature = "async"))]
    /// Creates an instance of this component using dependencies from given [ComponentInstanceProvider].
    fn create(
        instance_provider: &mut dyn ComponentInstanceProvider,
    ) -> Result<Self, ComponentInstanceProviderError>;

    #[cfg(feature = "async")]
    /// Creates an instance of this component using dependencies from given [ComponentInstanceProvider].
    fn create(
        instance_provider: &mut (dyn ComponentInstanceProvider + Sync + Send),
    ) -> BoxFuture<'_, Result<Self, ComponentInstanceProviderError>>;
}

/// Helper trait for traits implemented by components, thus allowing injection of components based
/// on `dyn Trait` types. The type `C` refers to a concrete component type. Typically automatically
/// derived when using the `#[component_alias]` attribute.
pub trait ComponentDowncast<C: Component>: Injectable {
    fn downcast(
        source: ComponentInstanceAnyPtr,
    ) -> Result<ComponentInstancePtr<Self>, ComponentInstanceAnyPtr>;
}

/// Marker trait for injectable types - components and aliases.
pub trait Injectable: 'static {}