PHP static scope redeclare

Question

I got this example when working with static scope in PHP function:

function testStatic() {
static $a;
echo "here is a first time: ".$a."<br />";
$a = 23;
static $a = 100;
echo "here is a second time: ".$a."<br />";
}

when I run this function like this

teststatic(); echo "<hr />";
teststatic();

It output result below:

here is a: 100
here is a: 23

---

here is a: 23
here is a: 23

But I expect it to be the following:

here is a: null
here is a: 100

---

here is a: 100
here is a: 100

I have been thinking hours try to explain why I received the result above but really failed. Could you tell me why we have the result above? Thank you!

Answer 1

It's hard to believe that the output you indicate is really the output of that code. Yet the problem is clear here:

A static variable is bound to a function or class and declared via the static keyword. You are re-declaring $a; this should (I guess) raise a warning.

As static properties are part of the function's or class' definition, (apparently) the last occurrence of it will be "attached" to the function/class in question.

Only the first time the function is called $a is assigned the value of 23. After the first echo statement.

This is a 2-step process, first the parser will read the function's definition, including static properties. After that the code will run, and the properties are mutated.