解决方法基本语法不被解析

问题描述

我想有一个类属性，允许的Ex pression发生在等号的右边签字。 PHP的所有版本都呛以下code，但它是用这种方式，以便在未来更容易扩展性。

I want to have a class property that allow for an expression to take place on the right side of the equals sign. All versions of PHP choke on the following code, but it is written in this way to allow for easier extendibility in the future.

/* Example SDK Class */
class SDK
{
    /* Runtime Option Flags */
    // Strings
    #  0: Makes no change to the strings.
    var $STRING_NONE        = (1 << 0);
    #  1: Removes color codes from the string.
    var $STRING_STRIP_COLOR = (1 << 1);
    #  2: Removes language codes from the string.
    var $STRING_STRIP_LANG  = (1 << 2);
    #  3: Removes all formatting from the string.
    var $STRING_STRIP       = SELF::STRING_STRIP_COLOR & SELF::STRING_STRIP_LANG;
    #  4: Converts color codes to HTML & UTF-8.
    var $STRING_HTML        = (1 << 3);
    #  8: Converts color codes to ECMA-48 escape color codes & UTF-8.
    var $STRING_CONSOLE     = (1 << 4);
    # 16: Changes player names only.
    var $STRING_NAMES       = (1 << 5);
    # 32: Changes host names only.
    var $STRING_HOSTS       = (1 << 6);
    function SDK($fString = SELF::STRING_HTML & SELF::STRING_NAMES & SELF_HOST)
    {
        // constructor code.
    }
}

$SDK &= new SDK(SDK::STRING_NONE);

（1 LT;℃下）看起来非常基本的语法我，是不是可测，为什么PHP不会允许这样的事情。谁能想到一个工作围绕将维持以下code的可读性和未来可扩展性？

(1 << 0) seems like very basic syntax to me, and is not fathomable why PHP would not allow for such a thing. Can anyone think of a work around that would maintain readability and future expandability of the following code?

推荐答案

在声明一个类PHP常量或属性，你只能指定默认值的原始值。因此，举例来说，此类声明是行不通的：

When declaring a class constant or property in PHP you can only specify a primitive values for default values. So for instance, this class declaration won't work:

class TEST {
 const ABC = 2 * 4;
 const DEF = some_function();
 static $GHI = array(
   'key'=> 5 * 3,
 );
}

但这个类声明将：

But this class declaration will:

class TEST {
 const ABC = 8;
 static $GHI = 15;
}

这些规则适用于的类常量/属性定义默认值的 - 你总是可以初始化其他变量和前pression的结果：

These rules apply to default values for class constants/properties - you can always initialize other variables with the results of an expression:

$a= array(
 'a'=> 1 * 2,
 'b'=> 2 * 2,
 'c'=> 3 * 2,
);

这样做的原因类声明的行为如下：前pressions就像动词。他们的做点什么的。类是像名词：他们的申报的东西的。声明性陈述不应该产生一个动作语句的副作用。需要原始缺省值强制执行这一规则。

The reason for this class declaration behavior is as follows: expressions are like verbs. They do something. Classes are like nouns: they declare something. A declarative statement should never produce the side-effects of an action statement. Requiring primitive default values enforces this rule.

考虑到这一点，我们可以重构原始类如下：

With this in mind we can refactor the original class as follows:

class SDK
{

    static protected $_types= null;

    static public function getType($type_name) {
        self::_init_types();
        if (array_key_exists($type_name, self::$_types)) {
            return self::$_types[$type_name];
        } else {
            throw new Exception("unknown type $type_name");
        }
    }

    static protected function _init_types() {
        if (!is_array(self::$_types)) {
            self::$_types= array(
                'STRING_NONE'=> 1 << 0,
                // ... rest of the "constants" here
                'STRING_HOSTS'=> 1 << 6
            );
        }
    }

    function __construct($fString = null) {
        if (is_null($fString)) {
            $fString= self::getType('STRING_NONE') & self::getType('STRING_HOSTS');
        }
        var_dump($fString);
    }

}

$SDK &= new SDK(SDK::getType('STRING_HOSTS'));

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