# LaunchDarkly Go SDK Evaluation Engine

[![Circle CI](https://circleci.com/gh/launchdarkly/go-server-sdk-evaluation.svg?style=shield)](https://circleci.com/gh/launchdarkly/go-server-sdk-evaluation) [![Documentation](https://img.shields.io/static/v1?label=go.dev&message=reference&color=00add8)](https://pkg.go.dev/github.com/launchdarkly/go-server-sdk-evaluation/v2)

## Overview

This repository contains the internal feature flag evaluation logic and data model used by the [LaunchDarkly Go SDK](https://github.com/launchdarkly/go-server-sdk). It is packaged separately because it is also used by internal LaunchDarkly components. Applications using the LaunchDarkly Go SDK should not need to reference this package directly.

## Supported Go versions

This version of the project requires a Go version of 1.18 or higher.

## Integration with easyjson

By default, `go-server-sdk-evaluation-private` uses LaunchDarkly's open-source JSON library [`go-jsonstream`](https://github.com/launchdarkly/go-jsonstream) to convert its data model types like `FeatureFlag` to and from JSON; this is considerably faster than Go's built-in `encoding/json` and does not depend on any third-party code. However, it can optionally integrate with the third-party library [`easyjson`](https://github.com/mailru/easyjson), which may be even faster in some cases, without requiring any changes in your code. To enable this, set the build tag `launchdarkly_easyjson` when you run `go build`, which both switches `go-jsonstream` to use `easyjson` internally and also generates `MarshalEasyJSON`/`UnmarshalEasyJSON` methods for each JSON-serializable type. The `easyjson` library is still under development and has some potential compatibility issues; see its documentation for more details.

If you do not set the `launchdarkly_easyjson` build tag, `go-server-sdk-evaluation` does not use any code from `easyjson`.

## Learn more

Check out our [documentation](http://docs.launchdarkly.com) for in-depth instructions on configuring and using LaunchDarkly. You can also head straight to the [complete reference guide for the Go SDK](http://docs.launchdarkly.com/docs/go-sdk-reference), or the [generated API documentation](https://pkg.go.dev/github.com/launchdarkly/go-server-sdk-evaluation/v2) for this project.

## Contributing

We encourage pull requests and other contributions from the community. Check out our [contributing guidelines](CONTRIBUTING.md) for instructions on how to contribute to this SDK.

## About LaunchDarkly

* LaunchDarkly is a continuous delivery platform that provides feature flags as a service and allows developers to iterate quickly and safely. We allow you to easily flag your features and manage them from the LaunchDarkly dashboard.  With LaunchDarkly, you can:
    * Roll out a new feature to a subset of your users (like a group of users who opt-in to a beta tester group), gathering feedback and bug reports from real-world use cases.
    * Gradually roll out a feature to an increasing percentage of users, and track the effect that the feature has on key metrics (for instance, how likely is a user to complete a purchase if they have feature A versus feature B?).
    * Turn off a feature that you realize is causing performance problems in production, without needing to re-deploy, or even restart the application with a changed configuration file.
    * Grant access to certain features based on user attributes, like payment plan (eg: users on the ‘gold’ plan get access to more features than users in the ‘silver’ plan). Disable parts of your application to facilitate maintenance, without taking everything offline.
* LaunchDarkly provides feature flag SDKs for a wide variety of languages and technologies. Check out [our documentation](https://docs.launchdarkly.com/docs) for a complete list.
* Explore LaunchDarkly
    * [launchdarkly.com](https://www.launchdarkly.com/ "LaunchDarkly Main Website") for more information
    * [docs.launchdarkly.com](https://docs.launchdarkly.com/  "LaunchDarkly Documentation") for our documentation and SDK reference guides
    * [apidocs.launchdarkly.com](https://apidocs.launchdarkly.com/  "LaunchDarkly API Documentation") for our API documentation
    * [blog.launchdarkly.com](https://blog.launchdarkly.com/  "LaunchDarkly Blog Documentation") for the latest product updates