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GoForjv0.9

Providers ​

A provider is a Go function Wire can call to construct a dependency.

Providers keep construction explicit: dependencies go in as parameters, and the constructed value comes out as the return value.

Shape ​

Most providers are constructors:

go
func NewService(repo *Repository, cache Cache) *Service {
	return &Service{
		repo:  repo,
		cache: cache,
	}
}

A provider can also return an error when construction can fail:

go
func ProvideGateway(cfg Config) (*Gateway, error) {
	if cfg.BaseURL == "" {
		return nil, errors.New("BILLING_API_URL is required")
	}

	return NewGateway(cfg), nil
}

Wire uses the return type to satisfy another constructor's parameter.

What Providers Build ​

Providers can build:

  • application services
  • repositories
  • controllers
  • commands
  • job handlers
  • managers
  • adapters and gateways
  • typed configuration values
  • runtime components

Keep the provider's job narrow: construct dependencies, choose implementations, and validate construction inputs.

What They Should Not Do ​

Providers should not hide runtime behavior.

Avoid:

  • business workflows
  • package globals
  • background workers started from random constructors
  • repeated environment reads from leaf services
  • nil fallbacks for required dependencies

Construction and runtime are separate. Long-running work should start through lifecycle hooks or runtime commands, not from provider functions.

Required Dependencies ​

Required dependencies should be visible in the constructor signature.

go
func NewService(repo *Repository, gateway *Gateway) *Service {
	return &Service{
		repo:    repo,
		gateway: gateway,
	}
}

If a dependency is optional, model the optional behavior directly. Do not make required wiring look optional just to avoid a Wire error.

Next Steps ​