Question

I am using PHP 5.3 on Ubuntu. I want to share a pair of code snippets and want to know the reason of such contradiction in order to initialize associated array.

Case 1: A part of class

class ui_template extends ui\ui_component{
   private $path = __DIR__."/templates";
   private $properties_template = array('path' => __DIR__.'/templates', 'file' => 'mytemplate.php', 'engine' => 'php'); // Parse error: syntax error, unexpected '.', expecting ')'
   private $properties_template = array('path' => $path, 'file' => 'mytemplate.php', 'engine' => 'php'); // Parse error: syntax error, unexpected T_VARIABLE, expecting T_FUNCTION

Case 2: A part of simple script

$path = __DIR__ . "/templates";
$temp = new widget\ui_template('new_template');
$temp->extend_template(NULL, array('path' => __DIR__."/templates")); // works fine
$temp->extend_template(NULL, array('path' => $path)); // works fine

• In the first case at line#3 that is strange to report an error on . while defining path, means concatenation is not allowed there. While in case 2 nothing such error.

• In the first case at line#4 a variable is also not allowed to initialized path

Answer 1

You can’t use computed values when declaring class properties. They must be constant (literal string, number, etc.). Docs:

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.