Development of Zend engine_PHP tutorial-PHP Tutorial-php.cn

Development of Zend engine_PHP tutorial

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Release： 2016-07-13 10:53:08

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In the last section of this chapter, Zeev discusses the object model brought by the Zend engine, especially how it is different from the models in previous versions of PHP.
When we developed PHP3 in the summer of 1997, we had no plan to make PHP object-oriented. There were no ideas about classes and objects at that time. PHP3 was a purely procedural language. However, on the night of August 27, 1997 Support for classes was added to the PHP3 alpha version. Adding a new feature to PHP required only minimal discussion at the time, because there were too few people exploring PHP at the time. So starting from August 1997, PHP took the step towards object-oriented The first step in programming languages.

Really, this is just the first step. Because there are very few relevant ideas in this design, the support for objects is not strong enough. Using objects in this version is just a cool way to access arrays. Instead of using $foo[ "bar"], you can use the prettier looking $foo->bar. The main advantage of the object-oriented approach is to store functionality through member functions or methods. A typical code block is shown in Example 6.18. But it It’s actually not much different from the approach in Example 6.19.

Listing 6.18 PHP 3 object-oriented programming Object-oriented programming in PHP3

class Example
{
var $value = "some value";
function PrintValue()
{
print $this->value;
}
}
$obj = new Example();
$obj->PrintValue();
?>
Listing 6.19 PHP 3 structural programming PHP3 Structured programming in PHP3

function PrintValue($arr)
{
print $arr["value"];
}

function CreateExample()
{
$arr["value"] = "some value";
$arr["PrintValue"] = "PrintValue";

return $arr;
}

$arr = CreateExample();

//Use PHP's indirect reference
$arr["PrintValue"]($arr);
?>
Above we write two lines of code in the class, or explicitly pass the array to the function. But considering that there is no difference between these two options in PHP3, we can still just treat the object model as a "syntactic gloss". Access array.

People who wanted to use PHP for object-oriented development, especially those who wanted to use design patterns, quickly found that they hit a wall. Fortunately, at the time (PHP3 era), not many people wanted to use PHP for object-oriented development.

PHP4 changed this situation. The new version brought the concept of reference, which allows different identifiers in PHP to point to the same address in memory. This means that you can use two or more names to Name the same variable, just like Example 6.20.

Listing 6.20 PHP 4 references References in PHP4

$a = 5;

//$b points to the same place in memory as $a $b and $a point to the same address in memory
$b = &$a;

//we're changing $b, since $a is pointing to change $b, the pointed address changes
//the same place - it changes too The address pointed to by $a also changes
$b = 7;

//prints 7 output 7
print $a;