In-depth study of the underlying development principles of PHP7: Understand the implementation mechanism of function calling and variable assignment

In-depth study of the underlying development principles of PHP7: Understand the implementation mechanism of function calls and variable assignments

Introduction:
PHP7 is a popular server-side programming language. It is widely used in web development, and for developers who want to deeply understand the underlying development principles of PHP7, it is crucial to understand the implementation mechanism of function calling and variable assignment. This article will focus on the implementation principles of function calling and variable assignment in PHP7, and provide in-depth analysis through code examples.

First, let’s understand the implementation mechanism of function calling in PHP7. In PHP7, the implementation of function calls is based on the stack data structure. When we call a function, the PHP compiler saves the context of the current function into a stack frame and creates a new stack frame for the called function. This stack frame contains information such as parameters and local variables of the called function. When the called function completes execution, the stack frame will be destroyed and control will return to the stack frame of the calling function.

The following is a sample code to demonstrate the creation and destruction process of stack frames when a function is called:

function foo($x) {
    $y = 3;
    $z = $x + $y;
    return $z;
}

function bar($a) {
    $b = 2;
    $c = foo($a + $b);
    return $c;
}

$result = bar(1);
echo $result;

In the above code, we define two functions - foo and bar, the bar function calls the foo function. When the bar function calls the foo function, a new stack frame is created to save the context of the foo function. After the foo function is executed, the stack frame will be destroyed and control returns to the stack frame of the bar function.

Next, we will introduce the implementation mechanism of variable assignment in PHP7. In PHP7, the implementation of variable assignment is based on reference counting. When we assign a value to a variable, PHP will create an internal structure for the variable to save the variable's value and reference count. When another variable references the same value, the reference count increases; when a variable no longer references the value, the reference count decreases. When the reference count reaches 0, the internal structure will be destroyed and the memory space will be released.

The following is a sample code to demonstrate the change process of the reference count when assigning a variable:

$a = 1;
$b = $a;

$c = $a + $b;
echo $c;

unset($a);
unset($b);

$d = $c + 2;
echo $d;

In the above code, we assign the value of the variable $a The variable $b is given, so $a and $b point to the same value. When variable $c uses $a and $b, the reference count is increased to 2. When we use the unset function to destroy the variables $a and $b, the reference count is reduced to 0, the internal structure is destroyed, and the memory space is released. When we add $c to the number 2, the reference count becomes the new 1.

Conclusion:
Through in-depth research on the underlying development principles of PHP7, we understand the implementation mechanism of function calling and variable assignment. The implementation of function calling is based on the stack data structure, while the implementation of variable assignment is based on reference counting. Understanding these underlying principles can help us better understand the operating mechanism of PHP7, optimize our code, and improve program performance.

Reference:

• PHP Internals Book: https://www.phpinternalsbook.com
• Zend Engine Internals: http://www.php-internals. com

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