Adding custom code

Fern-generated SDKs are designed to be extended with custom code. Your custom code can add additional functionality to the SDK and live in harmony with the generated code.

This page explains how to configure custom logic using a .fernignore file, create custom SDK methods, and add additional dependencies to your SDK.

Adding custom logic

If you want your SDK to do more than just make basic API calls (like combining multiple calls, processing data, adding utilities), you can use .fernignore to protect your custom code from being overwritten during regeneration.

Simply add your custom files to the SDK repository and list them out in .fernignore. Fern won’t override any files that you add in .fernignore.

To get started adding custom code:

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func MyHelper() {
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  fmt.Println("Hello World!")
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}

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# Specify files that shouldn't be modified by Fern
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helper.go

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import "github.com/package/example"
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example.MyHelper();

Adding custom SDK methods

Fern also allows you to add custom methods to the SDK itself (e.g. client.my_method() ) by inheriting the Fern generated client and then extending it.

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- name: fernapi/fern-go-sdk
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    version: "..."
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    config:
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      clientName: BaseClient

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type MyClient struct {
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  *Client // Embed the Fern generated client.
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}
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func NewMyClient(opts ...option.RequestOption) *MyClient {
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  return &MyClient{
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    Client: NewClient(opts...),
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  }
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}
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func (m *MyClient) MyHelper() {
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  fmt.Println("Hello World!")
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}

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+ client/my_client.go

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import exampleclient "github.com/package/example/client"
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client := exampleclient.NewMyClient():

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client.MyHelper()