PHP callback function (callback)

The following content is from the official Php.net document

Callbacks

Functions such as Call_user_func (), Usort () accept user-defined callback functions as parameters.

A callback function can be more than just a simple function, or it can be an object method, including a static method of an object.

PHP functions can be called by the function name of a string type, and any built-in or user-defined functions can be used. But that doesn't include

PHP language structure, such as: Array (), Echo,empty (), eval (), exit (), Isset (), List (), Print,unset ()

The method of invoking a class is called by using the name of the instantiated object and the calling method, respectively, as the No. 0 and 1th parameters of the array.

A static method that invokes a class can invoke the name of the class and the name of the static method as the No. 0 and 1th arguments of the array, respectively, without instantiating the object of the class.

After php5.2.3, you can also invoke the static method of the class by using Classname::methodname.

In addition to these generic user-defined functions, anonymous functions can also be used as function arguments.

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