PHP中的动态常量名称

Question

我试图动态创建一个常量名称,然后获取该值.

define( CONSTANT_1 , "Some value" ) ;

// try to use it dynamically ...
$constant_number = 1 ;
$constant_name = ("CONSTANT_" . $constant_number) ;

// try to assign the constant value to a variable...
$constant_value = $constant_name;

但是我发现$ constant值仍然包含常量的NAME,而不是VALUE.

我也尝试了第二级间接$$constant_name但是这会使它变量而不是常量.

有人可以对此有所了解吗？

Answer 1

http://dk.php.net/manual/en/function.constant.php

echo constant($constant_name);

Answer 2

并证明这也适用于类常量:

class Joshua {
    const SAY_HELLO = "Hello, World";
}

$command = "HELLO";
echo constant("Joshua::SAY_$command");

Answer 3

要在类中使用动态常量名称,可以使用反射功能(因为php5):

$thisClass = new ReflectionClass(__CLASS__);
$thisClass->getConstant($constName);

例如:如果要仅过滤类中的特定(SORT_*)常量

class MyClass 
{
    const SORT_RELEVANCE = 1;
    const SORT_STARTDATE = 2;

    const DISTANCE_DEFAULT = 20;

    public static function getAvailableSortDirections()
    {
        $thisClass = new ReflectionClass(__CLASS__);
        $classConstants = array_keys($thisClass->getConstants());

        $sortDirections = [];
        foreach ($classConstants as $constName) {
            if (0 === strpos($constName, 'SORT_')) {
                $sortDirections[] =  $thisClass->getConstant($constName);
            }
        }

        return $sortDirections;
    }
}

var_dump(MyClass::getAvailableSortDirections());

结果:

array (size=2)
  0 => int 1
  1 => int 2