yii2/docs/internals/bc.md

Backwards Compatibility

We're strictly not breaking backwards compatibility in patch releases such as 2.x.y.Z and trying to avoid had to fix backwards incompatible changes in minor releases such as 2.x.Y.

Check Yii Versioning to learn about version numbering.

Usage

Interfaces

Use case	BC?
Type hint with the interface	Yes
Call the interface method	Yes
Implement the interface and...
Implement method	Yes
Add argument to method implemented	Yes
Add default value to an argument	Yes

Classes

Use case	BC?
Type hint with the class	Yes
Create a new instance	Yes
Extend the class	Yes
Access a public property	Yes
Call a public method	Yes
Extend the class and...
Access a protected property	Yes
Call a protected method	Yes
Override a public property	Yes
Override a protected property	Yes
Override a public method	Yes
Override a protected method	Yes
Add a new property	No
Add a new method	No
Add an argument to an overridden method	Yes
Add a default value to an argument	Yes
Call a private method (via Reflection)	No
Access a private property (via Reflection)	No

Development

Changing interfaces

Type of change	BC?
Remove	No
Change name or namespace	No
Add parent interface	Yes if no new methods are added
Remove parent interface	No
Interface methods
Add method	No
Remove method	No
Change name	No
Move to parent interface	Yes
Add argument without a default value	No
Add argument with a default value	No
Remove argument	Yes (only last ones)
Add default value to an argument	No
Remove default value of an argument	No
Add type hint to an argument	No
Remove type hint of an argument	No
Change argument type	No
Change return type	No
Constants
Add constant	Yes
Remove constant	No
Change value of a constant	Yes except objects that are likely to be serialized. Mandatory to document in UPGRADE.md.

Classes

Type of change	BC?
Remove	No
Make final	No
Make abstract	No
Change name or namespace	No
Change parent class	Yes but original parent class must remain an ancestor of the class.
Add interface	Yes
Remove interface	No
Public Properties
Add public property	Yes
Remove public property	No
Reduce visibility	No
Move to parent class	Yes
Protected Properties
Add protected property	Yes
Remove protected property	No
Reduce visibility	No
Move to parent class	Yes
Private Properties
Add private property	Yes
Remove private property	Yes
Constructors
Remove constructor	No
Reduce visibility of a public constructor	No
Reduce visibility of a protected constructor	No
Move to parent class	Yes
Public Methods
Add public method	Yes
Remove public method	No
Change name	No
Reduce visibility	No
Move to parent class	Yes
Add argument without a default value	No
Add argument with a default value	No
Remove arguments	Yes, only last ones
Add default value to an argument	No
Remove default value of an argument	No
Add type hint to an argument	No
Remove type hint of an argument	No
Change argument type	No
Change return type	No
Protected Methods
Add protected method	Yes
Remove protected method	No
Change name	No
Reduce visibility	No
Move to parent class	Yes
Add argument without a default value	No
Add argument with a default value	No
Remove arguments	Yes, only last ones
Add default value to an argument	No
Remove default value of an argument	No
Add type hint to an argument	No
Remove type hint of an argument	No
Change argument type	No
Change return type	No
Private Methods
Add private method	Yes
Remove private method	Yes
Change name	Yes
Add argument without a default value	Yes
Add argument with a default value	Yes
Remove argument	Yes
Add default value to an argument	Yes
Remove default value of an argument	Yes
Add type hint to an argument	Yes
Remove type hint of an argument	Yes
Change argument type	Yes
Change return type	Yes
Static Methods
Turn non static into static	No
Turn static into non static	No
Constants
Add constant	Yes
Remove constant	No
Change value of a constant	Yes except objects that are likely to be serialized. Mandatory to document in UPGRADE.md.