将功能输出分配给功能参数？ [关闭]

Is it possible in PHP setup a predefined function parameter to be a result of another function?

function f1() { return rand().'entropy'; }

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function f2($a=f1(), $b=Null) {
    if($a==Null) $a='default';
    return $a.$b;
}

. . You can't assign it directly, but you can "emulate" it the same way you are doing with the "default" string:

function f1() { return rand().'entropy'; }

function f2($a = Null, $b=Null) {
    if ($a == Null) { $a = f1(); }
    if ($a == Null) { $a = 'default'; }
    return $a . $b;
}

. . Seeing that the f1() always returns a string, the second if in my code will never get executed. I just followed your code sample and as I understand this was just an example of how you can use the return of a function as a default value, ok?