有人可以为我清理静态变量吗？

Question

Using PHP here, I decided to read through the manual chapter by chapter and learn new things. So now I've discovered static variables, which seem like an awesome concept, but the way I understand it is:

Static variables are set once and only once per load of the script. They can be changed and incremented but not actually re-set. Usually used in functions to set a value and not have to initialize that variable every time the function runs.

<?php

function count2( $inputNum ) {
    static $a = $inputNum;
    echo $a++; //Echo and then increment.
}

for ( $i = 0; $i < 10; $i++ ) {
    count2(50);
}

?>

I'd expect this to start the static $a var at 50, and increment 11 times. How come I get an error?

Answer 1

The static variable cannot be initialized with another variable, whose value is not known until runtime. You must initialize it with a value known at compile time.

function count2($inputNum) {
  // Initialize only once to an integer (non variable, non-expression)
  static $a = 0;
  if ($a === 0) {
    // If $a is still 0, set it to $inputNum
    $a = $inputNum;
  }
  echo $a++;
}

// First run outputs 25
count2(25);
// 25
// Subsequent runs increment
count2(25);
// 26
count2(25);
// 27

Relevant documentation...