php 解析错误：语法错误，意外的“.”，期待“,”或“;”
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Parse error: syntax error, unexpected '.', expecting ',' or ';'
提问by Tejas Jadhav
This thing is bugging me a lot. I'm getting Parse error: syntax error, unexpected '.', expecting ',' or ';' at this line
这件事让我很烦恼。我收到解析错误：语法错误，意外的 '.'，期待 ',' 或 ';' 在这一行
public static $user_table = TABLE_PREFIX . 'users';
TABLE_PREFIX is a constant created by define function
TABLE_PREFIX 是由定义函数创建的常量
回答by Michael Berkowski
Static class properties are initialized at compile time. You cannot use a constant TABLE_PREFIXto concatenate with a string literal when initializing a static class property, since the constant's value is not known until runtime. Instead, initialize it in the constructor:
静态类属性在编译时初始化。TABLE_PREFIX初始化静态类属性时，不能使用常量与字符串文字连接，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
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.
像任何其他 PHP 静态变量一样，静态属性只能使用文字或常量进行初始化；不允许使用表达式。因此，虽然您可以将静态属性初始化为整数或数组（例如），但您不能将其初始化为另一个变量、函数返回值或对象。
Update for PHP >= 5.6
更新 PHP >= 5.6
PHP 5.6 brought limited support for expressions:
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.
在 PHP 5.6 及更高版本中，适用于 const 表达式的相同规则：一些有限的表达式是可能的，前提是它们可以在编译时计算。
回答by troelskn
The dot is a string concatenation operator. It's a runtime function, so it can't be used to declare a static (parsetime) value.
点是字符串连接运算符。它是一个运行时函数，因此不能用于声明静态（解析时间）值。
