@coderspirit/lambda-ioc

Pure functional (λ) dependency injection 💉 for TypeScript (inspired by Diddly)

NOTE: This is a “fork” of Tom Sherman’s Diddly library, who deserves most credit for this work.

Install instructions

Node

# With NPM
npm install @coderspirit/lambda-ioc

# Or with Yarn:
yarn add @coderspirit/lambda-ioc

Deno

Lambda-IoC is served through different CDNs

import { ... } from 'https://denopkg.com/Coder-Spirit/lambda-ioc@[VERSION]/lambda-ioc/deno/index.ts'
import { ... } from 'https://deno.land/x/lambda_ioc@[VERSION]/lambda-ioc/deno/index.ts'

Example

import {
  constructor,
  createContainer,
  func
} from '@coderspirit/lambda-ioc'

function printNameAndAge(name: string, age: number) {
  console.log(`${name} is aged ${age}`)
}

class Person {
  constructor(
    public readonly age: number,
    public readonly name: string
  ) {}
}
​
const container = createContainer()
  .registerValue('someAge', 5)
  .registerValue('someName', 'Timmy')
  // We can register functions
  .register('fn', func(printNameAndAge, 'someName', 'someAge'))
  // And constructors too
  .register('Person', constructor(Person, 'someAge', 'someName'))
  // We can "define groups" by using `:` as an infix, the group's name will be
  // the first part of the string before `:`.
  // Groups can be used in all "register" methods.
  .registerValue('group1:a', 1) // group == 'group1'
  .registerValue('group1:b', 2)
  .registerValue('group2:a', 3) // group == 'group2'
  .registerValue('group2:b', 4)
​
// We can resolve registered functions
const print = container.resolve('fn')
print() // Prints "Timmy is aged 5"

// We can resolve registered constructors
const person = container.resolve('Person')
console.print(person.age) // Prints "5"
console.print(person.name) // Prints "Timmy"

// We can resolve registered "groups"
container.resolveGroup('group1') // ~ [1, 2], not necessarily in the same order
container.resolveGroup('group2') // ~ [3, 4], not necessarily in the same order

// We can also resolve the container itself, and the return type will always be
// up to date. This is useful if we want to use the container as a factory for
// some of your dependencies.
const resolvedContainer = container.resolve('$')

It is also possible to register and resolve asynchronous factories and dependencies. If you are curious, just try out:

• registerAsync
• registerAsyncConstructor
• resolveAsync

Benefits

• 100% type safe:
  • The type checker will complain if we try to resolve unregistered dependencies.
  • The type checker will complain if we try to register new dependencies that depend on unregistered dependencies, or if there is any kind of type mismatch.
• Purely functional
• Immutable
• Circular dependencies are impossible

Drawbacks

• All dependencies must be declared “in order”.
  • This implies that this IoC container cannot be used in combination with some auto-wiring solutions, such as IoC decorators.
• The involved types are a bit convoluted:
  • They might cause the type checker to be slow.
  • In some situations, the type checker might be unable to infer the involved types due to excessive “nested types” depth.

Differences respect to Diddly

• First-class support for Deno.
• First-class support for asynchronous dependency resolution.
• Stricter types for dependencies re-registration.
• Groups registration and resolution: very useful when we need to resolve all dependencies belonging to a same category.
• Self-resolution. The container is able to resolve itself, to be used as a factory.
• The container interface has been split into ReaderContainer and WriterContainer, making it easier to use precise types.
• More extense documentation.