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[^2] |
| Override a protected method | No[^3] |
| Access a protected property | No[^4] |
| Call a public method | Yes |
| Override a public method | Yes[^5] |
| Override a public property | Yes |
| Add a public property | No |
| Add a public method | No |
| Add an argument | |
| to an overridden method | No[^6] |
| 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[^7] |
| Properties | |
| Add a public property | Yes |
| Remove a public property | No |
| Add a protected property | Yes |
| Remove a protected property | Yes[^8] |
| 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[^9] |
| Reduce visibility | No |
| Change method name | Yes[^10] |
| Add default value to | |
| existing argument | No |
| Add argument with | |
| default value | Yes |
| Add required argument | No |
[^1]: Your code may be broken by minor releases. Check the migration guide for details.
[^2]: Your code may be broken by minor releases. Check the migration guide for details.
[^3]: Your code may be broken by minor releases. Check the migration guide for details.
[^4]: Your code may be broken by minor releases. Check the migration guide for details.
[^5]: Your code may be broken by minor releases. Check the migration guide for details.
[^6]: Your code may be broken by minor releases. Check the migration guide for details.
[^7]: You can change a class/method name as long as the old name remains available. This is generally avoided unless renaming has significant benefit.
[^8]: Avoid whenever possible. Any removals need to be documented in the migration guide.
[^9]: Avoid whenever possible. Any removals need to be documented in the migration guide.
[^10]: You can change a class/method name as long as the old name remains available. This is generally avoided unless renaming has significant benefit.