Pseudotypes in PHP

1.mixed

mixed indicates that a parameter can accept multiple (but not necessarily all) different types.

3.callback

void as a return type means that the return value of the function is useless.

void as parameter list means the function does not accept any parameters.

In the function prototype, $... means etc.

Use this variable name when a function can accept any number of parameters.

The above introduces the pseudo-types in PHP, including aspects of the content. I hope it will be helpful to friends who are interested in PHP tutorials.