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Inheritance

Inheritance can be achieved as long as constructor parameters are properly decorated. There are two ways to ensure this:

  • The number of decorated constructor arguments in a derived class is greater than or equal to the number of constructor arguments in its base class.
  • The skipBaseClassChecks option is enabled.

Example of incorrect inheritance injection​

@injectable()
class Warrior {
  public rank: string;
  constructor(rank: string) { // args count = 1
    this.rank = rank;
  }
}

@injectable()
class SamuraiMaster extends Warrior {
  constructor() { // args count = 0
    super("master");
  }
}

When trying to get a SamuraiMaster, the container throws an error indicating that the constructor parameters are not properly decorated.

Using the @unmanaged decorator​

The unmanaged decorator tells Inversify that a base type constructor parameter should not be managed. This is often the case when dealing with inheritance hierarchies where only leaf types are injected.

@injectable()
class Warrior {
  public rank: string;
  constructor(@unmanaged() rank: string) { // args count = 0, unmanaged args are not included
    this.rank = rank;
  }
}

@injectable()
class SamuraiMaster extends Warrior {
  constructor() { // args count = 0
    super("master");
  }
}