Constructors

How a service’s constructor may be declared: a plain function, a method of another service, or a generic function instantiated with explicit type arguments. How each argument is spelled is covered in Arguments.

Constructor Signatures

A constructor — func or method — must return exactly one of:

1. T
2. (T, error)

T is any type the container can check statically: concrete types, pointers, slices, maps, channels, and interfaces with methods.

• A constructor returning any/interface{}, or a named type whose underlying type is an empty interface, is rejected at generation time: such a type makes every assignment valid and leaves nothing to verify
• Generic constructors require explicit type arguments, so a bare type parameter never becomes a service type
• Argument count and types are validated against the signature

Method Constructors

Use service methods to construct other services:

services:
  factory:
    constructor:
      func: "factory.New"
    shared: true

  processor:
    constructor:
      method: "@factory.CreateProcessor"
      args:
        - "@dependency"
    shared: false

Generated code:

func (c *Container) buildProcessor() (*Processor, error) {
    factory, err := c.getFactory()
    if err != nil {
        return nil, err
    }
    dep, err := c.getDependency()
    if err != nil {
        return nil, err
    }
    return factory.CreateProcessor(dep), nil
}

Generic Constructors

Support for Go generics with type arguments:

services:
  events:
    constructor:
      func: "github.com/gendi-org/gendi/stdlib.NewChan[github.com/myapp/events.Event]"
      args:
        - 100  # buffer size
    public: true

Generated code:

func (c *Container) buildEvents() (chan events.Event, error) {
    return make(chan events.Event, 100), nil
}

stdlib.NewChan is a real generic function of the stdlib package; the generator recognizes it and emits the equivalent make expression through a dedicated inliner instead of calling it, so the generated file does not import stdlib. A generic constructor from any other package is instantiated and called normally: pkg.NewPool[events.Event](100).