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

Deprecations are removed with the next major version of the framework. It is advised that you adapt to deprecations as they are introduced to ensure future upgrades are easier.

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. New methods may be added, but no existing methods will be changed.

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, 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 overridden methods with a differing signature you may see fatal 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…

Override a public property

Yes

Access a protected property

No 1

Override a protected property

No 1

Override a protected method

No 1

Call a protected method

No 1

Add a public property

No

Add a public method

No

Add an argument to an overridden method

No 1

Add a default argument value to an existing method argument

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 to parent class

Yes

Remove a protected method

Yes 3

Reduce visibility

No

Change method name

Yes 2

Add a new argument with default value

Yes

Add a new required argument to an existing method.

No

Remove a default value from an existing argument

No

Change method type void

Yes

1(1,2,3,4,5)

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.

Deprecations

In each minor release, features may be deprecated. If features are deprecated, API documentation and runtime warnings will be added. Runtime errors help you locate code that needs to be updated before it breaks. If you wish to disable runtime warnings you can do so using the Error.errorLevel configuration value:

// in config/app.php
// ...
'Error' => [
    'errorLevel' => E_ALL ^ E_USER_DEPRECATED,
]
// ...

Will disable runtime deprecation warnings.