Backwards Compatibility Guide

Ensuring that you can upgrade your applications easily and smoothly is important to us. That’s why we only break compatibility at major release milestones. You might be familiar with semantic versioning, which is the general guideline we use on all CakePHP projects. In short, semantic versioning means that only major releases (such as 2.0, 3.0, 4.0) can break backwards compatibility. Minor releases (such as 2.1, 3.1, 3.2) may introduce new features, but are not allowed to break compatibility. Bug fix releases (such as 2.1.2, 3.0.1) do not add new features, but fix bugs or enhance performance only.

Note

CakePHP started following semantic versioning in 2.0.0. These rules do not apply to 1.x.

To clarify what changes you can expect in each release tier we have more detailed information for developers using CakePHP, and for developers working on CakePHP that helps set expectations of what can be done in minor releases. Major releases can have as many breaking changes as required.

Migration Guides

For each major and minor release, the CakePHP team will provide a migration guide. These guides explain the new features and any breaking changes that are in each release. They can be found in the Appendices section of the cookbook.

Using CakePHP

If you are building your application with CakePHP, the following guidelines explain the stability you can expect.

Interfaces

Outside of major releases, interfaces provided by CakePHP will not have any existing methods changed and new methods will not be added to any existing interfaces.

Classes

Classes provided by CakePHP can be constructed and have their public methods and properties used by application code and outside of major releases backwards compatibility is ensured.

Note

Some classes in CakePHP are marked with the @internal API doc tag. These classes are not stable and do not have any backwards compatibility promises.

In minor releases (3.x.0), new methods may be added to classes, and existing methods may have new arguments added. Any new arguments will have default values, but if you’ve overidden methods with a differing signature you may see errors. Methods that have new arguments added will be documented in the migration guide for that release.

The following table outlines several use cases and what compatibility you can expect from CakePHP:

If you… Backwards compatibility?
Typehint against the class Yes
Create a new instance Yes
Extend the class Yes
Access a public property Yes
Call a public method Yes
Extend a class and…
Call a protected method No [1]
Override a protected property No [1]
Override a protected method No [1]
Access a protected property No [1]
Call a public method Yes
Override a public method Yes [1]
Override a public property Yes
Add a public property No
Add a public method No
Add an argument to an overridden method No [1]
Add a default argument to an existing method Yes

Working on CakePHP

If you are helping make CakePHP even better please keep the following guidelines in mind when adding/changing functionality:

In a minor release you can:

In a minor release can you…
Classes
Remove a class No
Remove an interface No
Remove a trait No
Make final No
Make abstract No
Change name Yes [2]
Properties
Add a public property Yes
Remove a public property No
Add a protected property Yes
Remove a protected property Yes [3]
Methods
Add a public method Yes
Remove a public method No
Add a protected method Yes
Move member to parent class Yes
Remove a protected method Yes [3]
Reduce visibility No
Change method name Yes [2]
Add default value to existing argument No
Add argument with default value Yes
Add required argument No
[1](1, 2, 3, 4, 5, 6) Your code may be broken by minor releases. Check the migration guide for details.
[2](1, 2) You can change a class/method name as long as the old name remains available. This is generally avoided unless renaming has significant benefit.
[3](1, 2) Avoid whenever possible. Any removals need to be documented in the migration guide.