PHP函数参数my_func（$ param =''）

I saw some PHP today I don't understand, can anyone explain it to me?

function my_func($param='')
{

    if (empty($param))
    {
        return false;
    }
    else
    {
        return true;
    }
}

What I don't understand is the $param variable being assigned an empty string but somehow not being empty inside the function? Is this just a default value?

my_func("string") //makes $param "string"

my_func() //picks default making $param ''

You can have required and optional params like

function my_func($param1, $param2='default')

You can NOT put optional params behind required params

function my_func($param1='', $param2) //gives errors.

Yes, you can assign a default value to a param in PHP. You can overwrite it using my_func("None Empty String") for example!

Your assumption was correct; this allows the developer to assign a default value to the parameter.

If the calling code does not pass a parameter value, the function returns false. Otherwise, $param is non-empty, and the function returns true.

A potential pitfall with this code is the case of a parameter being passed with an empty value (0, null, etc). The code will return false even though a parameter was passed.

Yes, the variable inside the parenthesis of the function declaration is a default value, and is used so you can call the function like this:

echo my_func();

Without needing to actually pass a variable to the function at all.