你不能在一个PHP类中放入两个具有唯一参数签名的__construct函数。我想这样做:
class Student
{
protected $id;
protected $name;
// etc.
public function __construct($id){
$this->id = $id;
// other members are still uninitialized
}
public function __construct($row_from_database){
$this->id = $row_from_database->id;
$this->name = $row_from_database->name;
// etc.
}
}
PHP中最好的方法是什么?
从5.4版开始,PHP支持trait。这并不是你真正想要的,但基于特征的简单方法是:
trait StudentTrait {
protected $id;
protected $name;
final public function setId($id) {
$this->id = $id;
return $this;
}
final public function getId() { return $this->id; }
final public function setName($name) {
$this->name = $name;
return $this;
}
final public function getName() { return $this->name; }
}
class Student1 {
use StudentTrait;
final public function __construct($id) { $this->setId($id); }
}
class Student2 {
use StudentTrait;
final public function __construct($id, $name) { $this->setId($id)->setName($name); }
}
我们最终得到两个类,每个构造函数一个,这有点适得其反。为了保持理智,我将加入一个工厂:
class StudentFactory {
static public function getStudent($id, $name = null) {
return
is_null($name)
? new Student1($id)
: new Student2($id, $name)
}
}
所以,这一切都归结为:
$student1 = StudentFactory::getStudent(1);
$student2 = StudentFactory::getStudent(1, "yannis");
这是一个非常冗长的方法,但它可以非常方便。
你总是可以在构造函数中添加一个额外的参数,比如mode,然后对它执行一个switch语句……
class myClass
{
var $error ;
function __construct ( $data, $mode )
{
$this->error = false
switch ( $mode )
{
'id' : processId ( $data ) ; break ;
'row' : processRow ( $data ); break ;
default : $this->error = true ; break ;
}
}
function processId ( $data ) { /* code */ }
function processRow ( $data ) { /* code */ }
}
$a = new myClass ( $data, 'id' ) ;
$b = new myClass ( $data, 'row' ) ;
$c = new myClass ( $data, 'something' ) ;
if ( $a->error )
exit ( 'invalid mode' ) ;
if ( $b->error )
exit ('invalid mode' ) ;
if ( $c->error )
exit ('invalid mode' ) ;
Also with that method at any time if you wanted to add more functionality you can just add another case to the switch statement, and you can also check to make sure someone has sent the right thing through - in the above example all the data is ok except for C as that is set to "something" and so the error flag in the class is set and control is returned back to the main program for it to decide what to do next (in the example I just told it to exit with an error message "invalid mode" - but alternatively you could loop it back round until valid data is found).
嗯,很惊讶我还没有看到这个答案,假设我要参加竞选。
class Action {
const cancelable = 0;
const target = 1
const type = 2;
public $cancelable;
public $target;
public $type;
__construct( $opt = [] ){
$this->cancelable = isset($opt[cancelable]) ? $opt[cancelable] : true;
$this->target = isset($opt[target]) ? $opt[target] : NULL;
$this->type = isset($opt[type]) ? $opt[type] : 'action';
}
}
$myAction = new Action( [
Action::cancelable => false,
Action::type => 'spin',
.
.
.
]);
您可以选择将这些选项分离到它们自己的类中,例如扩展脾。
abstract class ActionOpt extends SplEnum{
const cancelable = 0;
const target = 1
const type = 2;
}
正如这里已经展示的,在PHP中有许多方法来声明多个构造函数,但是没有一种方法是正确的(因为PHP技术上不允许这样做)。
但这并不能阻止我们破解这个功能……
下面是另一个例子:
<?php
class myClass {
public function __construct() {
$get_arguments = func_get_args();
$number_of_arguments = func_num_args();
if (method_exists($this, $method_name = '__construct'.$number_of_arguments)) {
call_user_func_array(array($this, $method_name), $get_arguments);
}
}
public function __construct1($argument1) {
echo 'constructor with 1 parameter ' . $argument1 . "\n";
}
public function __construct2($argument1, $argument2) {
echo 'constructor with 2 parameter ' . $argument1 . ' ' . $argument2 . "\n";
}
public function __construct3($argument1, $argument2, $argument3) {
echo 'constructor with 3 parameter ' . $argument1 . ' ' . $argument2 . ' ' . $argument3 . "\n";
}
}
$object1 = new myClass('BUET');
$object2 = new myClass('BUET', 'is');
$object3 = new myClass('BUET', 'is', 'Best.');
使用和理解多个构造函数的最简单方法:
希望这能有所帮助。:)
我可能会这样做:
<?php
class Student
{
public function __construct() {
// allocate your stuff
}
public static function withID( $id ) {
$instance = new self();
$instance->loadByID( $id );
return $instance;
}
public static function withRow( array $row ) {
$instance = new self();
$instance->fill( $row );
return $instance;
}
protected function loadByID( $id ) {
// do query
$row = my_awesome_db_access_stuff( $id );
$this->fill( $row );
}
protected function fill( array $row ) {
// fill all properties from array
}
}
?>
然后,如果我想要一个学生,我知道ID:
$student = Student::withID( $id );
或者如果我有一个db行数组:
$student = Student::withRow( $row );
从技术上讲,您不需要构建多个构造函数,而只是静态帮助方法,但是这样可以避免构造函数中的大量意大利面条代码。