Syrette

The convenient dependency injection & inversion of control framework for Rust.

Namesake

From the syrette Wikipedia article.

A syrette is a device for injecting liquid through a needle. It is similar to a syringe except that it has a closed flexible tube (like that typically used for toothpaste) instead of a rigid tube and piston.

Features

• A dependency injection and inversion of control container
• Autowiring dependencies
• API inspired from the one of InversifyJS
• Helpful error messages
• Supports generic implementations & generic interface traits
• Binding singletons
• Injection of third-party structs & traits
• Named bindings
• Async factories

Optional features

• factory. Binding factories (Rust nightly required)
• prevent-circular. Detection and prevention of circular dependencies. (Enabled by default)
• async. Asynchronous support

To use these features, you must enable it in Cargo.

Why inversion of control & dependency injection?

The reason for practing IoC and DI is to write modular & loosely coupled applications.

This is what we're trying to avoid:

impl Foo
{
    /// ❌ Bad. Foo knows the construction details of Bar.
    pub fn new() -> Self
    {
        Self {
            bar: Bar::new()
        }
    }

The following is better:

impl Foo
    /// ✅ Better. Foo is unaware of how Bar is constructed.
    pub fn new(bar: Bar) -> Self
    {
        Self {
            bar
        }
    }
}

This will however grow quite tiresome sooner or later when you have a large codebase with many dependencies and dependencies of those and so on. Because you will have to specify the dependencies someplace

let foobar = Foobar::new(
    Foo:new(
        Woof::new(),
        Meow::new()),
    Bar::new(
        Something::new(),
        SomethingElse::new(),
        SomethingMore::new()
    )
)

This is where Syrette comes in.

Motivation

Other DI & IoC libraries for Rust are either unmaintained (di for example), overcomplicated and requires Rust nightly for all functionality (anthill-di for example) or has a weird API (teloc for example).

The goal of Syrette is to be a simple, useful, convenient and familiar DI & IoC library.

Example usage

use std::error::Error;

use syrette::injectable;
use syrette::DIContainer;
use syrette::ptr::TransientPtr;

trait IWeapon
{
	fn deal_damage(&self, damage: i32);
}

struct Sword {}

#[injectable(IWeapon)]
impl Sword
{
	fn new() -> Self
	{
		Self {}
	}
}

impl IWeapon for Sword
{
	fn deal_damage(&self, damage: i32)
	{
		println!("Sword dealt {} damage!", damage);
	}
}

trait IWarrior
{
	fn fight(&self);
}

struct Warrior
{
	weapon: TransientPtr<dyn IWeapon>,
}

#[injectable(IWarrior)]
impl Warrior
{
	fn new(weapon: TransientPtr<dyn IWeapon>) -> Self
	{
		Self { weapon }
	}
}

impl IWarrior for Warrior
{
	fn fight(&self)
	{
		self.weapon.deal_damage(30);
	}
}

fn main() -> Result<(), Box<dyn Error>>
{
	let mut di_container = DIContainer::new();

	di_container.bind::<dyn IWeapon>().to::<Sword>()?;

	di_container.bind::<dyn IWarrior>().to::<Warrior>()?;

	let warrior = di_container.get::<dyn IWarrior>()?.transient()?;

	warrior.fight();

	println!("Warrior has fighted");

	Ok(())
}

For more examples see the examples folder.

Terminology

Transient
A type or trait that is unique to owner.

Singleton
A type that only has a single instance. The opposite of transient. Generally discouraged.

Interface
A type or trait that represents a type (itself in the case of it being a type).

Factory
A function that creates new instances of a specific type or trait.

Default factory
A function that takes no arguments that creates new instances of a specific type or trait.

Rust version requirements

Syrette requires Rust >= 1.62.1 to work. This is mainly due to the dependency on Linkme.

Todo

• Add support for generic factories

Contributing

You can reach out by joining the mailing list.

This is the place to submit patches, feature requests and to report bugs.