Pseudotypes and pseudovariables in PHP

1. Pseudo-types

There are three PHP pseudo-types, namely: 1, mixed type. 2. number digital type. 3. callbackCallback type.

1, mixed mixed type:

mixed indicates that a parameter can accept multiple different types, but not all types.

2, number numeric type:

The number parameter can accept integer integer type and floatFloating point type.

3, callback type:

For example, the call_user_func() function can receive a user-defined function as a parameter, which is php Abuilt-in function. The callback function can not only be a function, but also a method of an object and a method of a static class. Aphp functionis passed using the function namestring. Any built-in or user-defined function can be passed, except language structures such as array(), echo(), empty() ,eval(),exit(),isset(),list(),print(),unset(), etc.

If you want to pass in the method of an object, it needs to be passed in the form of an array. The array subscript 0 is the object name and the subscript 1 is the method name. If there is no static class instantiated as an object, to pass its method, replace the object name specified by the array 0 subscript with the name of the class.

In addition to ordinary user-defined functions, you can also use create_function to create an anonymouscallback function.

Example::

        

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2. Pseudo variables

$... in php is pseudo Variable means etc. This variable name is used when a function can accept any number of parameters.

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