PHP |预定义的类和接口

有一些类和接口可以是用户定义的，也可以用PHP语言预先定义。

PHP中有 9 个预定义的类和接口：

Traversable： Traversable 接口中没有方法，仅作为其他预定义 Traversable 类的基础。通过使用 foreach 构造和该接口，可以很容易地检测到该类是否可遍历。

迭代器：这是一个预定义的接口，用于对象或外部迭代器，它们能够进行内部迭代。该接口扩展了 Traversable 接口。该接口中的五个方法是：

Method name	parameters	return value	description
current	void	mixed	The present value is returned.
key	void	scalar	The present value’s key is returned.
next	void	void	Moving forward to the next element.
rewind	void	void	Set the position of the file pointer to the beginning of the file.
valid	void	bool	Check whether an array contains more entries or not.

IteratorAggregate：该接口是 Traversable 接口的扩展，只有一个方法。

method name	parameters	return type	description
getIterator	void	traversable	This function is used for retrieving an iterator(external).

此功能在PHP版本 7 中可用。通过 throw 语句抛出的所有对象都有一个接口，该接口充当称为 Throwtable 的基本接口。异常和错误类使用此接口。

Method name	name of arguments	return type	description
getMessage	void	string	Returns the message to be displayed when exception occurs.
getPrevious	void	throwtable	Previous exceptions are returned.
getCode	void	mixed	The code for exception generated.
getFile	void	string	The file in which exception occurs is returned.
getLine	void	int	The line number in which exception occurs returned.
getTrace	void	array	The stack trace is returned.
getTraceAsString	void	string	The stack trace is returned in the form of string.
__toString	void	string	The exception generated is returned in the form of string.

ArrayAccess：此接口允许将对象作为数组进行访问。它有4种方法：

method name	parameters	returns	description
offsetExists	offset value(mixed)	bool	Checks existence of the offset.
offsetGet	offset value(mixed)	mixed	The offset is retrieved through this method.
offsetSet	offset value(mixed), element(mixed)	void	A mentioned offset is given some value.
offsetUnset	offset value(mixed)	void	The value of offset is unset.

可序列化：此类允许以自定义方式进行序列化。如果需要对实例进行序列化，则调用方法 serialize()。如果它是在某个方法内的代码中编写的，则不会对程序进行任何更改或副作用。这个接口有两个方法：

method name	parameters	return	description
serialize	void	string	Object is converted into string.
unserialize	serialized string (string)	void	The object that was converted into string is converted back to an object.

闭包： PHP中有一些称为匿名函数的函数没有名称。回调参数被赋值为匿名函数。有5种方法：

method name	parameters	returns	description
__construct	void	void	A constructor disallowing instantiation
bind	object (closure) newthis (object)closure	closure	A closure can be duplicated by the class scope and mentioned particular bound object.
bindTo	newthis (object)closure	closure	A closure can be duplicated by the class scope and new bound object.
call	newthis (object)closure	mixed	The closure is binded and called.
fromCallable	Callable (Callable )	closure	The callable is converted into closure.

Generator：这个接口是Iterator的扩展，有9个方法：

method name	parameters	returns	descitption
current	void	mixed	The yielded element can be found.
getReturn	void	mixed	The generator’s value is returned by the function.
key	void	mixed	The key which was yielded is returned.
next	void	void	The generator’s execution is resumed.
rewind	void	void	The iterator is rewinded.
send	value(mixed)	mixed	A value is sent to the generator.
throw	exception(throwtable)	mixed	An exception is thrown into the generator.
valid	void	bool	Verifies if there was a closing of the iterator.
__wakeup	void	void	Callback is serialized.