Module shaku::guide

Getting started guide

Note: This getting started guide focuses on components, which live for the lifetime of the application (or, technically, the module). After reading this getting started guide, check out the provider guide to learn how to create services with shorter lifetimes.

Structure your application

Start with your application's structs and traits. Use Arc<dyn T> for dependencies.

use std::sync::Arc;

trait IOutput {
    fn write(&self, content: String);
}

trait IDateWriter {
    fn write_date(&self);
}

struct ConsoleOutput;

impl IOutput for ConsoleOutput {
    fn write(&self, content: String) {
        println!("{}", content);
    }
}

struct TodayWriter {
    output: Arc<dyn IOutput>,
    today: String,
    year: usize,
}

impl IDateWriter for TodayWriter {
    fn write_date(&self) {
        self.output.write(format!("Today is {}, {}", self.today, self.year));
    }
}

Inherit "Interface" for the interface traits

Interface traits require certain bounds, such as 'static and optionally Send + Sync if using the thread_safe feature. The Interface trait acts as a trait alias for these bounds, and is automatically implemented on types which implement the bounds.

In our example, the two interface traits would become:

use shaku::Interface;

trait IOutput: Interface {
    fn write(&self, content: String);
}

trait IDateWriter: Interface {
    fn write_date(&self);
}

Implement Component

A component is a struct that implements an Interface trait. In our example, we have 2 components:

• TodayWriter of type IDateWriter
• ConsoleOutput of type IOutput

These components must implement Component, which can either be done manually or through a derive macro (using the derive feature):

use shaku::Component;

#[derive(Component)]
#[shaku(interface = IOutput)]
struct ConsoleOutput;

Express dependencies

Components can depend on other components. In our example, TodayWriter requires an IOutput component.

To express this dependency, first make sure the property is declared as a trait object wrapped in an Arc. Then (when using the derive macro) use the #[shaku(inject)] attribute on the property to tell shaku to inject the dependency.

In our example:

use shaku::Component;

#[derive(Component)]
#[shaku(interface = IDateWriter)]
struct TodayWriter {
    #[shaku(inject)]
    output: Arc<dyn IOutput>,
    today: String,
    year: usize,
}

If you don't use the derive macro, add HasComponent bounds to your module generic and inject the dependencies manually with HasComponent::build_component.

Define a module

Modules link together components and providers, and are core to providing shaku's compile time guarentees. A Module can be defined manually or via the module macro (the derive feature is not necessary):

use shaku::module;

module! {
    MyModule {
        components = [ConsoleOutput, TodayWriter],
        providers = []
    }
}

This module implements HasComponent<dyn IOutput> and HasComponent<dyn IDateWriter> using the provided component implementations.

Build the module

At application startup, start building the module using the generated builder method (created by the module macro). Alternatively, use ModuleBuilder::with_submodules to create the builder. Then, call ModuleBuilder::build to get the module instance.

let module = MyModule::builder().build();

Passing parameters

In many cases you need to pass parameters to a component. This can be done during module creation. Each component has an associated parameters type, and the derive generates a *Parameters struct for you (named after the component struct). Use this struct to pass in the parameters.

Note that if you don't pass in parameters, the parameters' default values will be used. You can override the default value by annotating the property with #[shaku(default = ...)].

let module = MyModule::builder()
    .with_component_parameters::<TodayWriter>(TodayWriterParameters {
        today: "Jan 26".to_string(),
        year: 2020
    })
    .build();

Resolve components

Once you created the module, you can resolve the components using the module's HasComponent methods.

use shaku::HasComponent;

let writer: &dyn IDateWriter = module.resolve_ref();
writer.write_date(); // Prints "Today is Jan 26, 2020"

Overriding components

Although shaku is a compile time DI library, you can override the implementation of a service during the module build. This can be useful during testing, for example using an in-memory database while doing integration tests. For components, simply pass in a struct instance which implements the interface you want to override to with_component_override:

#[derive(Component)]
#[shaku(interface = IOutput)]
struct FakeOutput;

impl IOutput for FakeOutput {
    fn write(&self, _content: String) {
        // We don't want to actually log stuff during tests
    }
}

let module = MyModule::builder()
    .with_component_override::<dyn IOutput>(Box::new(FakeOutput))
    .with_component_parameters::<TodayWriter>(TodayWriterParameters {
        today: "Jan 26".to_string(),
        year: 2020
    })
    .build();

let writer: &dyn IDateWriter = module.resolve_ref();
writer.write_date(); // Nothing will be printed

The full example

use shaku::{module, Component, Interface, HasComponent};
use std::sync::Arc;

trait IOutput: Interface {
    fn write(&self, content: String);
}

trait IDateWriter: Interface {
    fn write_date(&self);
}

#[derive(Component)]
#[shaku(interface = IOutput)]
struct ConsoleOutput;

impl IOutput for ConsoleOutput {
    fn write(&self, content: String) {
        println!("{}", content);
    }
}

#[derive(Component)]
#[shaku(interface = IDateWriter)]
struct TodayWriter {
    #[shaku(inject)]
    output: Arc<dyn IOutput>,
    today: String,
    year: usize,
}

impl IDateWriter for TodayWriter {
    fn write_date(&self) {
        self.output.write(format!("Today is {}, {}", self.today, self.year));
    }
}

module! {
    MyModule {
        components = [ConsoleOutput, TodayWriter],
        providers = []
    }
}

let module = MyModule::builder()
    .with_component_parameters::<TodayWriter>(TodayWriterParameters {
        today: "Jan 26".to_string(),
        year: 2020
    })
    .build();

let writer: &dyn IDateWriter = module.resolve_ref();
writer.write_date();

Modules

provider	Getting started with providers
submodules	Getting started with submodules