//! # aerosol
//! Simple dependency injection for Rust
//!
//! The two main exports of this crate are the `define_context`
//! and `define_interface` macros.
//!
//! Contexts are containers for multiple dependencies, allowing
//! them to be passed around as one with relative ease. Interfaces
//! are specialized traits which place constraints on contexts,
//! indicating exactly what dependencies a context must provide.
//!
//! Contexts are typically created at the top level of an application,
//! as they specify exactly what concrete versions of all dependencies
//! are going to be used. A single context is created with a precise
//! set of depenencies, and is then threaded through the rest of the
//! application as a generic parameter.
//!
//! Interfaces are used at every level of an application, as they
//! allow each piece of code to independently specify what dependencies
//! are required. Interfaces can "inherit" the dependencies of other
//! interfaces, with the idea being that this inheritance will form
//! a tree, such that there will be some "root interface" which contains
//! the union of all dependencies required by the whole application.
//!
//! This pattern allows dependencies to be added or removed from any
//! part of the application without having to modify the code at every
//! level, to thread or un-thread the new or old dependencies through.
//!
//! ## Example
//!
//! ```
//! #![recursion_limit="128"]
//! use std::sync::Arc;
//! use std::fmt::Debug;
//!
//! // We will depend on some kind of logger
//! trait Logger: Debug {
//! fn log(&self, msg: &str);
//! }
//!
//! // We have a specific implementation of a stdout logger
//! #[derive(Debug)]
//! struct StdoutLogger;
//!
//! impl Logger for StdoutLogger {
//! fn log(&self, msg: &str) {
//! println!("{}", msg);
//! }
//! }
//!
//! struct StdoutLoggerFactory;
//! impl aerosol::Factory for StdoutLoggerFactory {
//! type Object = Arc<Logger>;
//! fn build(_: ()) -> Result<Arc<Logger>, anyhow::Error> {
//! Ok(Arc::new(StdoutLogger))
//! }
//! }
//!
//! // Part of our application does some work
//! aerosol::define_interface!(
//! WorkerInterface {
//! fn logger(&self) -> Arc<Logger>;
//! }
//! );
//!
//! fn do_work<I: WorkerInterface>(iface: I) {
//! iface.logger().log("Doing some work!");
//! }
//!
//! // Our application does multiple pieces of work
//! aerosol::define_interface!(
//! AppInterface: WorkerInterface + Clone {}
//! );
//!
//! fn run_app<I: AppInterface>(iface: I, num_work_items: usize) {
//! for _ in 0..num_work_items {
//! do_work(iface.clone());
//! }
//! }
//!
//! // At the very top level, we specify the implementations
//! // of our dependencies.
//! aerosol::define_context!(
//! AppContext {
//! logger: Arc<Logger> [StdoutLoggerFactory],
//! }
//! );
//!
//! let context = AppContext::new().unwrap();
//!
//! run_app(context, 4);
//! ```
//!
//! See the individual macro documentation for more details.
pub extern crate tt_call;
/// The building block for this crate. Automatically implemented
/// for contexts providing a dependency of type `T`.
///
/// Super-trait of all interfaces requiring a dependency of type
/// `T`.
/// Implement this trait to provide a convenient syntax for
/// constructing implementations of dependencies.
/// Allows cloning a context whilst replacing one dependency
/// with a different implementation. Must be explicitly listed
/// as a super-trait of an interface to use.