Deprecation: #78733 - CallUserFunction "&" token for singleton objects¶
See Issue #78733
GeneralUtility::callUserFunction() allows to send the callee (the user-defined function)
to be prepended with a "&" before the method name to add the instantiated object to a "singleton" pool
during a single request. This functionality has been marked as deprecated as it can easily be solved by
implementing a class as singleton.
This way, the object is always a singleton, even when it is called via
callUserFunction() with a "&" symbol will trigger a deprecation log entry.
Any installation with a hook or user function which is registered with an ampersand "&" symbol.
The class of the user function / method can implement the
SingletonInterface to achieve the same behaviour.