Relearn PHP

PHP7 release也一段時間了,最近在開發常會看到相關的文章,最近抽個空好好來重新學習PHP.

Preface

“PHP: Hypertext Preprocessor”,官方網站表明PHP很適合做web development,但是並不局限於此,亦可做Process Control,但是依據個人經驗,PHP5.3以下的版本做浮點數的運算不是很精準.

另外在2015年PHP7問世,效率更是翻倍,但是有著相容性問題,系統升級前需要做好測試.

環境建置

採用Virtualbox+Vagrant來架設環境,執行步驟如下:

安裝Virtualbox與Vagrant,這邊就不講解了,幾本上下一步到底

下載Vagrant box

$ vagrant box add rasmus/php7dev
$ vagrant init rasmus/php7dev
# 確認box list
$ vagrant box list

git clone

git clone https://github.com/rlerdorf/php7dev.git
cd php7dev

共享目錄設定,編輯php7dev.yaml檔案

folders:
- map: www
  to: /var/www/default

啟動VM、進入VM、暫停VM、註銷VM

# 啟動VM
$ vagrnat up
# 進入VM
$ vagrant ssh
# 暫停VM
$ vagrant halt
# 註銷VM
$ vagrant destroy --force

建立檔案

# 建立一個 index.php 檔案, 運行可以顯示 PHP 資訊
$ echo "<?php echo phpinfo(); ?>" > /var/www/default/index.php

環境建立完成,再來可以透過Browser輸入http://192.168.7.7/來進入站台.

Type

PHP是屬於弱型別的語言,也就是變數不用宣告就直接可以做assign,但是資料型態還是程式語言的重點基礎之一,還是要好好的認識一下.

Boolean:通常是一個常量true或false,不區分大小寫.
```
$var1 = true;
$var2 = False;
```

Integer:是一個有限整數((2^32)-1),集合中的某個數Z = {…, -2, -1, 0, 1, 2, …}

//自PHP5.4.0後可以採用十進制、十六進制、八進制、二進制
$var = 1234; //十進制
$var = -123; //負數
$var = 0123; //八進制
$var = 0x1A; //十六進制
$var = 0b11111111; //二進制

Float:也就是小數,長度取決於平台. 另外不要相信浮點數結果精確到了最後一位,也永遠不要比較兩個浮點數是否相等,如果確實需要更高的精度,應該使用任意精度數學函數或者gmp函數.
```
$var = 1.23456789;
```

String:每個字都是由一系列的character(字元)組成(字的編碼),每個字元相當於一個byte(2^8),也就是說PHP只支援到256-character,因此不支援Unicode(因為過長).

$name = 'ting';
$var = 'my name is $name'; //全視為為字串
$var = "my name is $name"; //對$name進行解析
//Heredoc結構,自PHP5.3起,會對變數進行解析
$var = <<<EOT
my name is $name
    EOT;
//newcode結構,全視為字串,不對變數進行解析
$var = <<<'EOT'
my name is $name
    EOT;

Array:是一組有序映射,官網說"it can be treated as an array, list (vector), hash table (an implementation of a map), dictionary, collection, stack, queue, and probably more.",由此可見他的功能很廣.
```
$array = array(
    "foo" => "bar",
);
// 自 PHP 5.4 起
$array = [
    "foo" => "bar",
];
```

Object:物件.

class foo
{
    function do_foo()
    {
        echo "Doing foo.";
    }
}
$bar = new foo;
$bar->do_foo();

Resource:資源,通常可能是連接資料庫、開啟文件.
NULL:指一個變數還未被assign,或著被釋放
```
$var = NULL;
```

Callback

error_reporting(E_ALL);
function increment(&$var)
{
    $var++;
}
$a = 0;
call_user_func('increment', $a);
echo $a."\n";
call_user_func_array('increment', array(&$a));
echo $a."\n";

Variables

變數的命名很重要,程式要寫的漂亮的重點之一就是變數的命名.

基本變數:PHP中宣告變數是使用符號*$*後面再跟上’^[a-zA-Z][_]?[\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*’,且命名是有大小寫的區別.
```
$var = 'Bob';
$bar = &$var; //$bar被assign變數$var,且記憶體位置相同
```

全域變數與區域變數

$a = 1;
function Test()
{
    global $a;
    $b = 2;
    echo ($a+$b);
}
echo $b; //Undefined variable
Test();

Static variable:靜態變數只會在函數中出現,當程序離開函式,其值不丟失.從下面範例可以發現,在$b被宣告時,都還是NULL的狀態,宣告後才會取回值.
```
function Test()
{
    var_dump($b);
    static  $b = 0;
    var_dump($b);
    echo (++$b);
}
Test();
```

Variable variables:變數的名稱也是變數,這樣的特性讓程式變得更彈性.

$a = 'hello';
$hello = 'world';
$world = 'a';
echo $a.'<br/>';
echo $$a.'<br/>';
echo $$$a.'<br/>';
echo "$a ${$a} <br/>";
echo "$a $hello <br/>";

Constants

常量定義好後,就無法變更,且長量名稱區分大小寫.

define("version","0.1");
//magic constants
function a(){
    echo __function__;
}
function b(){
    echo __function__;
}
echo a();
echo b();

Operators

運算子有先後順序,個人習慣將運算子拆開,一來確保程式的穩定度,二來增加程式的可讀性

$a = true ? 0 : true ? 1 : 2; // (true ? 0 : true) ? 1 : 2 = 2
$a = 1;
$b = 2;
$a = $b += 3; // $a = ($b += 3) -> $a = 5, $b = 5

算數運算子

echo (5 + 3)."\n"; //prints 8
echo (5 - 3)."\n"; //prints 2
echo (5 * 3)."\n"; //prints 15
echo (15 / 3)."\n"; //prints 5
echo (5 % 3)."\n"; //prints 2
echo (5  3)."\n"; //prints 125

位元運算子

echo 0b0010 & 0b0010; //print 2
echo 0b0010 | 0b0010; //print 2
echo 0b0010 ^ 0b0011; //print 1
echo ~0b0101; //print -6
echo 0b0010 >> 1; //print 1
echo 0b0010 << 1; //print 4

比較運算子

var_dump(0 == "a"); //0 == 0 -> true
var_dump("1" == "01"); //1 == 1 -> true
var_dump("10" == "1e1"); //10 == 10 -> true
var_dump(100 == "1e2"); //100 == 100 -> true
var_dump("1e1"); //string '1e1'

錯誤控制運算子

@include('./not_exist_file.php');
$x = @$a["name"];

Execution Operators:以前都用exec(),這個好方便

$mkdir = `mkdir new floder`;
$output = `ls -al`;
echo "<pre>$output</pre>";

遞增/遞減運算子

$a = 5;
echo $a++."<br />"; //print 5
echo ++$a."<br />"; //print 7
echo $a--."<br />"; //print 7
echo --$a."<br />"; //print 5

Logical Operators

//"||" 比 "or" 的優先级高,"&&" 比 "and" 的優先级高
$e = false || true; //bool(true),等同于：($e = (false || true))
$f = false or true; //bool(false),等同于：(($f = false) or true)
$g = true && false; //bool(false),等同于：($g = (true && false))
$h = true and false; //bool(true),等同于：(($h = true) and false)

String Operators

$a = "Hello ";
$b = $a . "World!"; // now $b contains "Hello World!"
$a = "Hello ";
$a .= "World!";     // now $a contains "Hello World!"

Array Operators

$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");
$c = $a + $b; // Union of $a and $b
var_dump($c); // print array(3) {["a"]=>"apple",["b"]=>"banana",["c"]=>"cherry"}

Type Operators

class ParentClass{}
class MyClass extends ParentClass{}
$a = new MyClass;
var_dump($a instanceof MyClass); //bool(true)
var_dump($a instanceof ParentClass); //bool(true)

Control Structures

通常要呈現一個商業邏輯都會透過流程控制來表示,而每種商業邏輯呈現的方法百百種,所以要築構一支好的程式,對流程控制的熟悉度不可少.

if else

if ($a > $b):
    echo "a is bigger than b";
elseif ($a < $b):
    echo "a is smaller than b";
else:
    echo "a is equal b";
endif

while:循環語法之一,在遞迴中很好用

while ($i <= 10):
    echo $i++;
endwhile

do-while:跟while很像,差異在於while在執行前做判斷,do-while在執行後做判斷.
```
do {
   echo $i;
} while ($i <= 10);
```

for

for (;;):
    if ($i > 10):
        break;
    endif;
    echo $i;
    $i++;
endfor;

foreach:用來解構array很好用

foreach (array(1, 2, 3, 4) as $value):
    $value = $value * 2;
endforeach;

break

$arr = array('one', 'two', 'three', 'four', 'stop', 'five');
while (list (, $val) = each($arr)) {
    if ($val == 'stop') {
        break;    /* You could also write 'break 1;' here. */
    }
    echo "$val<br />\n";
}

continue

for ($i = 0; $i < 5; ++$i) {
    if ($i == 2)
        continue;
    print "$i\n";
}

switch:在做Boolean值判斷的時候建議使用if else,若做值得判斷則可使用switch

switch ($i) {
    case 0:
        echo "i equals 0";
        break;
    case 1:
    case 2:
        echo "i equals to 1, 2";
        break;
    default:
        echo "i is not equal to 0, 1 or 2";
}

declare:Zend引擎每執行1條低級語句就去執行一次register_tick_function()注冊的函數

declare(ticks=1);
// A function called on each tick event
function tick_handler() {
    echo "tick_handler() called\n";
}
register_tick_function('tick_handler');
$a = 1;
if ($a > 0) {
    $a += 2;
    print($a);
}

return:如果在全局範圍中調用,則當前腳本文件中止運行.

require/include/require_once/include_once

require('somefile.php'); //若找不到檔案發出E_COMPILE_ERROR级别錯誤,並終止程序
include('somefile.php'); //若找不到檔案發出E_WARNING级别錯誤,繼續程序
require_once('somefile.php'); //和require一樣,但已經包含過的檔案則不會再包含
include_once('somefile.php'); //和include一樣,但已經包含過的檔案則不會再包含

goto:只在PHP 5.3以上版本有效,跳轉至改文件的目標.目標位置只能位於同一個文件和作用域,也就是說無法跳出一個函數或類方法,也無法跳入到另一個函數.也無法跳入到任何循環或者switch結構中.可以跳出循環或者switch,通常的用法是用goto代替多層的break.
```
//下面結果輸出Bar
goto a;
echo 'Foo';
a:
echo 'Bar';
```

Function

這邊要注意部分預設函式是跟著extension加載的,例如mysql_connect()、imagecreatetruecolor()等,所以必須知道自己的環境是否有這些extension,可以用phpinfo()或get_loaded_extensions()來查詢. 函數名稱的命名很重要,好的命名可以讓程式可讀性提升,更好維護.

User-defined functions

function sum($a, $b): float {
    return $a + $b;
}

Variable functions

function foo() {
    echo "In foo()<br />\n";
}
$func = 'foo';
$func(); //This calls foo()

Anonymous functions

echo preg_replace_callback('~-([a-z])~', function ($match) {
    return strtoupper($match[1]);
}, 'hello-world');

Classes and Objects

自從PHP5後的版本有著較好的效能與功能

class:每個類別都有自己的constants、variables與function,並且可使用$this來調用自己.

class SimpleClass
{
    // property declaration
    public $var = 'a default value';
    // method declaration
    public function displayVar() {
        echo $this->var;
    }
}

Object Assignment:宣告物件的兩種方式.

Class Object{
   public $foo="bar";
};
$objectVar = new Object();
$reference =& $objectVar;
$assignment = $objectVar;
$objectVar=null;
var_dump($objectVar); //NULL
var_dump($reference); //NULL,指向同樣的記憶體,所以$objectVar=null被註銷時,一併註銷
var_dump($assignment); //object(Object),被clone

extends:一個class可以申明繼承另一個class的方法與屬性,不支援多個繼承.可以使用同名稱覆蓋父類別的方法,但是父類別使用final,則不能被覆蓋.被覆蓋的方法或屬性,可以透過parent::來訪問.
```
class ExtendClass extends SimpleClass
{
    // Redefine the parent method
    function displayVar()
    {
        echo "Extending class\n";
        parent::displayVar();
    }
}
```

Properties,類別的成員.

class SimpleClass
{
   public $var1 = (1+2);
   public $var2 = myConstant;
   public $var3 = array(true, false);
}

Class Constants:在類別中不變的值.

class MyClass
{
    const constant = 'constant value';
    function showConstant() {
        echo  self::constant . "\n";
    }
}

Autoloading Classes:可以不用透過include檔案來加載類別,可以透過__autoload()或spl_autoload_register() 函数自動註冊類別.

spl_autoload_register(function ($class_name) {
    require_once $class_name . '.php';
});
$obj  = new MyClass1();
$obj2 = new MyClass2();

Constructors and Destructors,在創建時會先調用__construct,註銷或程序結束時會調用__destruct.

class MyDestructableClass {
   function __construct() {
       print "In constructor\n";
       $this->name = "MyDestructableClass";
   }
   function __destruct() {
       print "Destroying " . $this->name . "\n";
   }
}
$obj = new MyDestructableClass();
unset($obj);

Visibility:包含public、protected、private.

class MyClass
{
    public $public = 'Public';
    protected $protected = 'Protected';
    private $private = 'Private';
    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}
$obj = new MyClass();
echo $obj->public; //public
echo $obj->protected; //產生錯誤
echo $obj->private; //產生錯誤
$obj->printHello(); //印出Public、Protected和Private

Scope Resolution Operator(::):用於訪問類別的靜態成員、常量或函式.

class MyClass {
    const CONST_VALUE = 'A constant value';
}
echo MyClass::CONST_VALUE;

Class Abstraction:繼承抽象類別的子類別,強制要求一定要有父類別定義的抽象函式的實作.這樣的好處是統一子類別中的實作格式.

abstract class AbstractClass
{
    //抽象方法僅需要定義需要的参数
    abstract protected function prefixName($name);
}
class ConcreteClass extends AbstractClass
{
    //子類別可以定義父類別抽象方法中不存在的可選参数
    public function prefixName($name, $separator = ".") {
        if ($name == "Pacman") {
            $prefix = "Mr";
        } elseif ($name == "Pacwoman") {
            $prefix = "Mrs";
        } else {
            $prefix = "";
        }
        return "{$prefix}{$separator} {$name}";
    }
}
$class = new ConcreteClass;
echo $class->prefixName("Pacman"), "\n"; //Mr. Pacman
echo $class->prefixName("Pacwoman"), "\n"; //Mrs. Pacwoman

Object Interfaces,透過implements導入多個介面接口,只能定義方法,但不能實作.

interface iTemplate
{
    public function setVariable($name, $var);
    public function getHtml($template);
}
class Template implements iTemplate
{
    private $vars = array();
    public function setVariable($name, $var)
    {
        $this->vars[$name] = $var;
    }
    public function getHtml($template)
    {
        foreach($this->vars as $name => $value) {
            $template = str_replace('{' . $name . '}', $value, $template);
        }
        return $template;
    }
}

Class Abstraction(抽象類別)與Object Interfaces(介面)的差異性如下面表格.

	類別(Class)	抽象類別(Abstract Class)	介面(Interface)
宣告屬性(attribute)	O	O	X
常數(const)	O	O	O
實例化(new class)	O	X	X
抽象方法(abstract function)	X	O	O
實作方法內容(functoin())	O	O	X
類別是否可繼承多個	X	X	O

Trait:自PHP5.4.0起可使用.介於繼承與介面之間的功能,可以參考Trait.

trait PrivateTrait
{
    private privateFunc()
    {
        echo "This is private";
    }
}
class PrivateClass
{
    use privateTrait;
    // This is allowed.
    public publicFunc()
    {
        $this->privateFunc();
    }
}

Anonymous classes.PHP7開始支持匿名類別.匿名類別可以創建一次性的簡單對象.

Overloading:動態創建成員與方法.

public void __set ( string $name , mixed $value )
public mixed __get ( string $name )
public bool __isset ( string $name )
public void __unset ( string $name )

class PropertyTest {
    private $data = array();
    public $declared = 1;
    private $hidden = 2;
    public function __set($name, $value)
    {
        $this->data[$name] = $value;
    }
    public function __get($name)
    {
        if (array_key_exists($name, $this->data)) {
            return $this->data[$name];
        }
        $trace = debug_backtrace();
        trigger_error(
            'Undefined property via __get(): ' . $name .
            ' in ' . $trace[0]['file'] .
            ' on line ' . $trace[0]['line'],
            E_USER_NOTICE);
        return null;
    }
    public function __isset($name)
    {
        return isset($this->data[$name]);
    }
    public function __unset($name)
    {
        unset($this->data[$name]);
    }
    public function getHidden()
    {
        return $this->hidden;
    }
}
$obj = new PropertyTest;
$obj->a = 1;
echo $obj->a; //1
var_dump(isset($obj->a)); //true
unset($obj->a);
var_dump(isset($obj->a)); //false

Magic Methods
- __sleep()
- __wakeup()
- __construct()
- __destruct()
- __call()
- __callStatic()
- __get()
- __set()
- __isset()
- __unset()
- __sleep()
- __wakeup()
- __toString()
- __invoke()
- __set_state()
- __clone()
- __debugInfo()