php - 解析错误 : syntax error, unexpected '.' expecting ',' or ';'

Question

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关闭 9 年前。

这件事一直困扰着我。我收到 Parse error: syntax error, unexpected '.', expecting ',' or ';'在这一行

public static $user_table = TABLE_PREFIX . 'users';

TABLE_PREFIX 是由定义函数创建的常量

Answer 1

静态类属性在编译时初始化。在初始化静态类属性时，不能使用常量 TABLE_PREFIX 与字符串文字连接，因为常量的值直到运行时才知道。相反，在构造函数中初始化它:

public static $user_table;

// Initialize it in the constructor 
public function __construct() {
  self::$user_table = TABLE_PREFIX . 'users';
}

// If you only plan to use it in static context rather than instance context 
// (won't call a constructor) initialize it in a static function instead 
public static function init() {
  self::$user_table = TABLE_PREFIX . 'users';
}

http://us2.php.net/manual/en/language.oop5.static.php

Like any other PHP static variable, static properties may only be initialized using a literal or constant; expressions are not allowed. So while you may initialize a static property to an integer or array (for instance), you may not initialize it to another variable, to a function return value, or to an object.

PHP 更新 >= 5.6

PHP 5.6 对表达式的支持有限:

In PHP 5.6 and later, the same rules apply as const expressions: some limited expressions are possible, provided they can be evaluated at compile time.