php英文文献翻译及参考文献 第4页

php英文文献翻译及参考文献 第4页
can be intermingled. PHP also supports strings, which can be used with single quotes, double quotes, or heredoc syntax.
The Standard PHP Library (SPL) attempts to solve standard problems and implements efficient data access interfaces and classes.
PHP has hundreds of base functions and thousands more via extensions. These functions are well documented on the PHP site, but unfortunately, the built-in library has a wide variety of naming conventions and inconsistencies. PHP currently has no functions for thread programming.
Functions are not first-class functions and can only be referenced by their name--directly or dynamically by a variable containing the name of the function. User-defined functions can be created at any time without being prototyped. Functions can be defined inside code blocks, permitting a run-time decision as to whether or not a function should be defined. Function calls must use parentheses, with the exception of zero argument class constructor functions called with the PHP new operator, where parentheses are optional. PHP supports quasi-anonymous functions through the create_function() function, although they are not true anonymous functions because anonymous functions are nameless, but functions can only be referenced by name, or indirectly through a variable $function_name();, in PHP.
PHP gained support for first-class functions and closures. True anonymous functions are supported using the following syntax:
function getAdder($x)
{
    return function ($y) use ($x) {
        return $x + $y;
    };
}

$adder = getAdder(8);
echo $adder(2); // prints "10"
Here, getAdder() function creates a closure using parameter $x (keyword "use" forces getting variable from context), which毕业论文http://www.751com.cn, etc. For more details see Lambda functions and closures RFC.
Basic object-oriented programming functionality was added in PHP 3 and improved in PHP 4.[3] Object handling was completely rewritten for PHP 5, expanding the feature set and enhancing performance. In previous versions of PHP, objects were handled like primitive types. The drawback of this method was that the whole object was copied when a variable was assigned or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value. PHP 5 introduced private and protected member variables and methods, along with abstract classes and final classes as well as abstract methods and final methods. It also introduced a standard way of declaring constructors and destructors, similar to that of other object-oriented languages such as C++, and a standard exception handling model. Furthermore, PHP 5 added interfaces and allowed for multiple interfaces to be implemented. There are special interfaces that allow objects to interact with the runtime system. Objects implementing ArrayAccess can be used with array syntax and objects implementing Iterator or IteratorAggregate can be used with the foreach language construct. There is no virtual table feature in the engine, so static variables are bound with a name instead of a reference at compile time.
If the developer creates a copy of an object using the reserved word clone, the Zend engine will check if a __clone() method has been defined or not. If not, it will call a default __clone() which will copy the object's properties. If a __clone() method is defined, then it will be responsible for setting the necessary properties in the created object. For convenience, the engine will supply a function that imports the properties of the source object, so that the programmer can start with

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