调用常量会产生难以理解的解析错误

Question

i am blocked by an incomprehensible syntax error that makes me crazy :/

The error displayed is Parse error: syntax error, unexpected '.', expecting ',' or ';'

This is the code that makes that:

class FamillePieceControllerCore extends FrontController
{
    public $php_self = 'famille-piece.php';

    private $webservice_url = _CICERONE_CONNECT_BASE_URL_ . 'WSC003&P2=0';
}

Where _CICERONE_CONNECT_BASE_URL_ is defined in a other file.

If i delete . 'WSC003&P2=0' the code works fine.

I don't understand :/ Thanks for helping

ps: I use php 5.3.8

Answer 1

You cannot initialize a class property with an expression (like concatenation). Instead you must do it in the constructor:

class FamillePieceControllerCore extends FrontController
{
    public $php_self = 'famille-piece.php';

    private $webservice_url;
    public function __construct() {
      $this->webservice_url = _CICERONE_CONNECT_BASE_URL_ . 'WSC003&P2=0';
    }
}

From the documentation:

Class member variables are called "properties". You may also see them referred to using other terms such as "attributes" or "fields", but for the purposes of this reference we will use "properties". They are defined by using one of the keywords public, protected, or private, followed by a normal variable declaration. 

This declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

Constants defined with define() are defined at runtime, so the value of _CICERONE_CONNECT_BASE_URL_ isn't known at compile time when the property is initialized.

Update for later PHP versions:

Beginning with PHP 5.6, simple expressions are permitted in class property declarations as long as they can still be evaluated at compile time. So the original posted code would compile and execute correctly in PHP 5.6+. Anything requiring runtime evaluation, such as a function call or variable interpolation is still not permitted.

// This is okay in PHP 5.6+
public $property = SOME_CONST . " other stuff";

// This is still not possible since
public $property = strlen(SOME_CONST);