CODEWITHSUNDEEP
go
kentor
kentor

Reputation: 18524

Extending a library's struct/interface

Use case

I am using Shopify's sarama libary which is a client library. More specifically I am using the ClusterAdmin struct which is great, however I want to add another method ListDetailedTopics to it and I must call ClusterAdmin's non public methods.

https://github.com/Shopify/sarama/blob/master/admin.go

Problem

I am not sure how I could "extend" the exported struct by my own method. I tried this:

func (ca *sarama.ClusterAdmin) ListDetailedtopics() {
  b, err := ca.findAnyBroker() // This is a private method I need to call
}

That did not work because "invalid receiver type *sarama.ClusterAdmin (sarama.ClusterAdmin is an interface type)". How can I extend the struct/interface by my own methods?

Upvotes: 1

Views: 418

Answers (1)

ifnotak
ifnotak

Reputation: 4662

You cannot extend the interface outside its package.

What you can do instead is define a new interface that implements the old interface and then add your new method to the new interface. For example:

type ExtendedClusterAdmin interface {
   sarama.ClusterAdmin
   ListDetailedtopics()
}

If you want to use private function within the package then you would have to do it inside the package itself. For example, with a patch.

Upvotes: 5

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