inject-macro

Experimental IOC library inspired by injector for Rust. Goals: IOC + ergonomics.

See test suite for all supported usages.

Examples

using #[inject], call!, get! and container!.

1. Configure a container, add some provider, e.g an Arc

   use std::sync::Arc;
   
   use ::inject::*;
   
   struct Instance(pub isize);
   
   impl Instance {
       #[inject]
       fn new(a: isize) -> Self {
           Instance(a)
       }
   }
   
   fn main() {
       let provider = Arc::new(Instance(3));
       
       // Install the Arc as a reference provider, anytime using get!
       // will resolve to a reference of this Arc.
       let container = container![
           ref provider
       ];
   
       let instance: &Instance = get!(&container, &Instance).unwrap();
       
       assert_eq!(3, instance.0)
   }
   

2. Let the container resolve a dependency, using a closure as provider

   use ::inject::*;
   
   struct Instance(pub isize);
   
   impl Instance {
       #[inject]
       fn new(a: isize) -> Self {
           Instance(a)
       }
   }
   
   struct Service {
       a: Instance
   }
   
   impl Service {
       #[inject]
       fn new(instance: Instance) -> Self {
           Self { a: instance }
       }
   }
   
   
   fn main() {
       // Install a provider, this time a closure returning a value
       let container = container![
           |container: &Container| Ok(Instance(2))
       ];
   
       let service: Service = get!(&container, Service).unwrap();
       
       assert_eq!(service.a.0, 2)
   }
   

3. Sometimes, calling a function with injection is useful,

   use ::inject::*;
   
   struct Service(isize);
   
   impl Service {
      #[inject]
      fn new() -> Self {
          Self(0)
      }
   }
   
   #[inject]
   fn acts_on_service(service: Service) -> isize {
      2 + service.0
   }
   
   fn main() {
      let container = container![
          |container: &Container| Ok(Service(3))
      ];
   
      let result = call!(&container, acts_on_service).unwrap();
   
      assert_eq!(result, 5)
   }
   

4. call! supports a kwarg-flavored syntax

   use ::inject::*;
   
   struct Service(isize);
   
   impl Service {
      #[inject]
      fn new() -> Self {
          Self(0)
      }
   }
   
   #[inject]
   fn acts_on_service(service: Service) -> isize {
      2 + service.0
   }
   
   fn main() {
      let container = container![];
   
      let result = call!(&container, acts_on_service, kwargs = { service: Service(2) }).unwrap();
   
      assert_eq!(result, 4)
   }
   

5. Dependency resolution can rely upon a type implementing the Default trait

   use ::inject::*;
   
   #[derive(Default)]
   struct Service(isize);
   
   fn main() {
      let container = container![];
      
      let service = get!(&container, Service).unwrap();
      
      assert_eq!(service.0, 0)
   }
   

Details

The get! macro with a container resolves a type in order of: installed provider (1), calling the associated inject function (often generated with #[inject]) function on a type (2), and lastly the Default trait (3).

(2) & (3) can be opt-out by attribute #[inject(no_inject(arg))], (name tbd) in which case only container held provider will be used for resolution of the type. Method specific defaults are annotated as #[inject(defualt(arg = expression))] where expression will lazy evaluate on failing attempt at (1) and (2).

Todo:

1. Support kwargs for "constructors" with a create_object! flavored macro.
2. Make #[inject] support Struct attribute notation with #[inject(..)] for individual struct fields.
3. Make default and no_inject story less annoying.