Macro create_udtf_function 

macro_rules! create_udtf_function {
    ($module:expr, $func_name:ident, $name:expr) => { ... };
}

Creates a singleton instance of a table function

• $module: A struct implementing TableFunctionImpl to create the function from
• $name: The name to give to the created function
• $func_name: The name of the function to be called This is used to ensure creating the list of TableFunction only happens once.