How Can I Register Go Packages Without Creating Cyclic Dependencies?

Registering Packages in Go without Cyclic Dependency

Registering packages in Go without cyclic dependency can be a challenge when different packages have dependencies on each other. This issue arises when a central package provides interfaces, while dependent packages offer implementations of those interfaces.

Solutions

1. Without a Central Registry:

In this approach, concrete implementations are defined in separate packages, and the central package simply declares the interface. When a specific implementation is required, it is explicitly instantiated, such as md5.New() or sha256.New(). This solution promotes separation and eliminates cyclic dependencies.

2. With a Central Registry:

This method involves creating a registration mechanism where implementations register themselves with the central package. The central package can then provide a lookup feature to select and create appropriate implementations. The image package in Go utilizes this approach, dynamically loading image decoders based on image format registrations.

3. Custom Registry:

A third option is to create a custom registry in a separate package that acts as an intermediary between the interface and implementations. This approach allows for a central "factory" method to create instances while maintaining package separation. For instance, an interface could reside in package pi, implementations in packages pa and pb, and a registry package pf would provide the pf.NewClient() factory method.

Ultimately, the choice of approach depends on the specific requirements of the project. If the implementation selection is known or static, using a custom registry is not necessary. However, for dynamic extension and extensibility, a registry mechanism provides flexibility and organization.

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