php - Parse error: syntax error, unexpected '.', expecting ',' or ';'

This thing is bugging me a lot. I'm getting Parse error: syntax error, unexpected '.', expecting ',' or ';' at this line

public static $user_table = TABLE_PREFIX . 'users';

TABLE_PREFIX is a constant created by define function

Answer

Static class properties are initialized at compile time. You cannot use a constant TABLE_PREFIX to 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:

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.

Update for PHP >= 5.6

PHP 5.6 brought limited support for expressions:

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.