PHP英文翻译

英文部分：When Zeev Suraski added the object-oriented syntax back in the days of PHP 3, it was added as "syntactic sugar for accessing collections." The OO model also had support for inheritance and allowed a class (and object) to aggregate both methods and properties, but not much more. When Zeev and Andi Gutmans rewrote the scripting engine for PHP 4, it was a completely new engine; it ran much faster, was more stable, and boasted more features. However, the OO model first introduced in PHP 3 was barely touched.Although the object model had serious limitations, it was used extensively around the world, often in large PHP applications. This impressive use of the OOP paradigm with PHP 4, despite its weaknesses, led to it being the main focus for the PHP 5 release.So, what were some of the limitations in PHP 3 and 4? The biggest limitation (which led to further limitations) was the fact that the copy semantics of objects were the same as for native types. So, how did this actually affect the PHP developer? When assigning a variable (that points to an object) to another variable, a copy of the object would be created. Not only did this impact performance, but it also usually led to obscure behavior and bugs in PHP 4 applications because many developers thought that both variables would point at the same object, which was not the case. The variables were instead pointing at separate copies of the same object. Changing one would not change the other.For example:class Person {var $name;function getName(){return $this->name;}function setName($name){$this->name = $name;}function Person($name){$this->setName($name);}}function changeName($person, $name){$person->setName($name);}$person = new Person("Andi");changeName($person, "Stig");print $person->getName();In PHP 4, this code would print out "Andi". The reason is that we pass the object $person to the changeName() function by-value, and thus, $person is copied and changeName() works on a copy of $person.This behavior is not intuitive, as many developers would expect the Java-like behavior. In Java, variables actually hold a handle (or pointer) to the object, and therefore, when it is copied, only the handle (and not the entire object) is duplicated.There were two kinds of users in PHP 4: the ones who were aware of this problem and the ones who were not. The latter would usually not notice this problem and their code was written in away where it did not really matter if the problem existed. Surely some of these people had sleepless nights trying to track down weird bugs that they could not pinpoint. The former group dealt with this problem by always passing and assigning objects by reference. This would prevent the engine from copying their objects, but it would be a headache because the code included numerous & signs.The old object model not only led to the afore-mentioned problems, but also to fundamental problems that prevented implementing some additional features on top of the existing object model.In PHP 5, the infrastructure of the object model was rewritten to work with object handles. Unless you explicitly clone an object by using the clone keyword, you never create behind-the-scenes duplicates of your objects. In PHP 5, you don't need a need to pass objects by reference or assign them by reference.NotePassing by reference and assigning by reference are still supported, in case you want to actually change a variable's content (whether object or other type).XML support in PHP 4 was implemented using a variety of underlying XML libraries. SAX support was implemented using the old Expat library, XSLT was implemented using the Sablotron library (or using libxml2 via the DOM extension), and DOM was implemented using the more powerful libxml2 library by the GNOME project.Using a variety of libraries did not make PHP 4 excel when it came to XML support. Maintenance was poor, new XML standards were not always supported, performance was not as good as it could have been, and interoperability between the various XML extensions did not exist.In PHP 5, all XML extensions have been rewritten to use the superb libxml2 XML toolkit . It is a feature-rich, highly maintained, and efficient implementation of the XML standards that brings cutting-edge XML technology to PHP.All the afore-mentioned extensions (SAX, DOM, and XSLT) now use libxml2, including the new additional extensions SimpleXML and SOAP.SAXAs previously mentioned, the new SAX implementation has switched from using Expat to libxml2. Although the new extension should be compatible, some small subtle differences might exist. Developers who still want to work with the Expat library can do so by configuring and building PHP accordingly (which is not recommended).DOMAlthough DOM support in PHP 4 was also based on the libxml2 library, it had bugs, memory leaks, and in many cases, the API was not W3C-compliant. The DOM extension went through a thorough facelift for PHP 5. Not only was the extension mostly rewritten, but now, it is also W3C-compliant. For example, function names now use studlyCaps as described by the W3C standard, which makes it easier to read general W3C documentation and implement what you have learned right away in PHP. In addition, the DOM extension now supports three kinds of schemas for XML validation: DTD, XML schema, and RelaxNG.As a result of these changes, PHP 4 code using DOM will not always run in PHP 5. However, in most cases, adjusting the function names to the new standard will probably do the trick.XSLTIn PHP 4, two extensions supported XSL Transformations: the Sablotron extension and the XSLT support in the DOM extension. PHP 5 features a new XSL extension and, as previously mentioned, it is based on the libxml2 extension. As in PHP 5, the XSL Transformation does not take the XSLT stylesheet as a parameter, but depends on the DOM extension to load it. The stylesheet can be cached in memory and may be applied to many documents, which saves execution time.SimpleXMLWhen looking back in a year or two, it will be clear that SimpleXML revolutionized the way PHP developers work with XML files. Instead of having to deal with DOM oreven worseSAX, SimpleXML represents your XML file as a native PHP object. You can read, write, or iterate over your XML file with ease, accessing elements and attributes.Consider the following XML file:<clients><client><name>John Doe</name><account_number>87234838</account_number></client><client><name>Janet Smith</name><account_number>72384329</account_number></client></clients>The following code prints each client's name and account number:$clients = simplexml_load_file('clients.xml');foreach ($clients->client as $client) {print "$client->name has account number $client >account_number\n";}It is obvious how simple SimpleXML really is.In case you need to implement an advanced technique in your SimpleXML object that is not supported in this lightweight extension, you can convert it to a DOM tree by calling it dom_import_simplexml(), manipulate it in DOM, and convert it to SimpleXML using simplexml_import_dom().Thanks to both extensions using the same underlying XML library, switching between them is now a reality.SOAPPHP 4 lacked official native SOAP support. The most commonly used SOAP implementation was PEARs, but because it was implemented entirely in PHP, it could not perform as well as a built-in C extension. Other available C extensions never reached stability and wide adoption and, therefore, were not included in the main PHP 5 distribution.SOAP support in PHP 5 was completely rewritten as a C extension and, although it was only completed at a very late stage in the beta process, it was incorporated into the default distribution because of its thorough implementation of most of the SOAP standard.The following calls SomeFunction() defined in a WSDL file:$client = new SoapClient("some.wsdl");$client->SomeFunction($a, $b, $c);From 《Php 5 Power Programming》翻译：当Zeev Suraski在过去的PHP 3时期增加面对对象语法的时候，面对对象是作为“访问集合的语法甜点”增加进去的。