Php declare function

- Php declare function if not exists
- Php declare function return type
- Php declare function once
- Php declare function as variable
- Php declare function parameter type
- Php declare function optional parameter
- Php declare global function
- Php declare abstract function
- Php declare function inside function
- Php declare variable type in function
- Php declare global variable inside function
- Php declare static function
- Php declare variable outside function
- Php declare array as function parameter
- Php declare class in function