How can you design backwards-compatible software interfaces?

1 Use semantic versioning

Semantic versioning is a convention for naming and numbering software releases that indicates the level of changes and compatibility between them. The basic format is MAJOR.MINOR.PATCH, where MAJOR changes are incompatible with previous versions, MINOR changes are compatible but add new features, and PATCH changes are compatible and fix bugs. By following semantic versioning, you can communicate clearly to your users and developers what to expect from each release and how to update their dependencies accordingly.

2 Avoid breaking changes

Breaking changes are modifications to a software interface that make it incompatible with previous versions or dependent components. Breaking changes can cause unexpected errors, crashes, or loss of functionality for your users and developers. Some examples of breaking changes are removing or renaming features, changing the order or type of parameters, altering the behavior or output of functions, or introducing new dependencies or requirements. To avoid breaking changes, you should follow the principle of least surprise, which means that your interface should behave consistently and predictably, and not introduce any surprises or changes that are not documented or announced.

3 Provide deprecation warnings

Sometimes, you may need to make breaking changes to your software interface for valid reasons, such as improving performance, security, or usability. However, you should not do so abruptly or without warning. Instead, you should provide deprecation warnings, which are messages that inform your users and developers that a feature or function is obsolete and will be removed or replaced in a future release. Deprecation warnings give your users and developers time to prepare for the change and update their code accordingly. You can provide deprecation warnings in various ways, such as documentation, comments, logs, or exceptions.

4 Use feature flags

Feature flags are conditional statements that enable or disable certain features or functions of your software interface based on some criteria, such as user preferences, environment variables, or configuration settings. Feature flags allow you to test and release new features gradually and safely, without affecting the existing functionality or compatibility of your interface. You can use feature flags to enable or disable features for different groups of users, such as beta testers, early adopters, or specific segments. You can also use feature flags to roll back features in case of errors or bugs.

5 Support multiple versions

Another way to design backwards-compatible software interfaces is to support multiple versions of your interface simultaneously. This means that you can offer different versions of your interface for different users or developers, depending on their needs and preferences. For example, you can offer a legacy version of your interface for users who do not want to upgrade or who rely on older features, and a modern version of your interface for users who want to access the latest features and improvements. You can also offer a transitional version of your interface that supports both the old and the new features, and helps users and developers migrate smoothly from one version to another.

6 Document your interface

Finally, one of the most important aspects of designing backwards-compatible software interfaces is to document your interface thoroughly and clearly. Documentation is the source of information and guidance for your users and developers, and it helps them understand how to use your interface correctly and efficiently. Documentation should include the description, purpose, parameters, return values, examples, and errors of each feature or function of your interface. It should also include the version, release date, changelog, and compatibility notes of your interface. Documentation should be updated regularly and consistently, and it should be easy to access and read.