在函数参数中转换数据类型？

Question

Does anyone know why it fails?

<?php 
function data((string)$data)
{
echo $data;

}

data(123);

Here is the error:

Parse error: syntax error, unexpected T_STRING_CAST, expecting '&' or T_VARIABLE in x.php on line 3

Answer 1

What your are trying to do is called: Type Hinting.

That is allowing a function or class method to dictate the type of argument it recieves.

Static type hinting was only introduced in PHP7 so using a version greater than that you can achieve whay you want with the following:

<?php

function myFunction(string $string){
    echo $string;
}

Now any non string argument passed to myFunction will throw an error.