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12 years ago
11/14/2016 - note updated by sobak

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CONSTANTS and PHP Class Definitions



Using "define('MY_VAR', 'default value')" INSIDE a class definition does not work as expected. You have to use the PHP keyword 'const' and initialize it with a scalar value -- boolean, int, float, string (or array in PHP 5.6+) -- right away.



<?php



define('MIN_VALUE', '0.0');   // RIGHT - Works OUTSIDE of a class definition.

define('MAX_VALUE', '1.0');   // RIGHT - Works OUTSIDE of a class definition.



//const MIN_VALUE = 0.0;         RIGHT - Works both INSIDE and OUTSIDE of a class definition.

//const MAX_VALUE = 1.0;         RIGHT - Works both INSIDE and OUTSIDE of a class definition.



class Constants

{

  //define('MIN_VALUE', '0.0');  WRONG - Works OUTSIDE of a class definition.

  //define('MAX_VALUE', '1.0');  WRONG - Works OUTSIDE of a class definition.



  const MIN_VALUE = 0.0;      // RIGHT - Works INSIDE of a class definition.

  const MAX_VALUE = 1.0;      // RIGHT - Works INSIDE of a class definition.



  public static function getMinValue()

  {

    return self::MIN_VALUE;

  }



  public static function getMaxValue()

  {

    return self::MAX_VALUE;

  }

}



?>



#Example 1:

You can access these constants DIRECTLY like so:

 * type the class name exactly.

 * type two (2) colons.

 * type the const name exactly.



#Example 2:

Because our class definition provides two (2) static functions, you can also access them like so:

 * type the class name exactly.

 * type two (2) colons.

 * type the function name exactly (with the parentheses).



<?php



#Example 1:

$min = Constants::MIN_VALUE;

$max = Constants::MAX_VALUE;



#Example 2:

$min = Constants::getMinValue();

$max = Constants::getMaxValue();



?>



Once class constants are declared AND initialized, they cannot be set to different values -- that is why there are no setMinValue() and setMaxValue() functions in the class definition -- which means they are READ-ONLY and STATIC (shared by all instances of the class).
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