I'm trying to access a class constant in one of my classes:
const MY_CONST = "value";
If I have a variable which holds the name of this constant like this:
$myVar = "MY_CONST";
Can I access the value of MY_CONST somehow?
self::$myVar
does not work obviously because it is for static properties. Variable variables does not work either.
There are two ways to do this: using the constant function or using reflection .
The constant function works with constants declared through define
as well as class constants:
class A
{
const MY_CONST = 'myval';
static function test()
{
$c = 'MY_CONST';
return constant('self::'. $c);
}
}
echo A::test(); // output: myval
A second, more laborious way, would be through reflection:
$ref = new ReflectionClass('A');
$constName = 'MY_CONST';
echo $ref->getConstant($constName); // output: myval
There is no syntax for that, but you can use an explicit lookup:
print constant("classname::$myConst");
I believe it also works with self::
.
Can I access the value of MY_CONST somehow?
self::MY_CONST
If you want to access is dynamically, you can use the reflection API Docs :
$myvar = 'MY_CONST';
$class = new ReflectionClass(self);
$const = $class->getConstant($myVar);
The benefit with the reflection API can be that you can get all constants at once ( getConstants
).
If you dislike the reflection API because you don't wanna use it, an alternative is the constant
function ( Demo ):
$myvar = 'MY_CONST';
class foo {const MY_CONST = 'bar';}
define('self', 'foo');
echo constant(self.'::'.$myvar);
你有没有尝试过
$myVar = MY_CONST or $myVar = $MY_CONST
Just a note for Reflection: the constructor for ReflectionClass must receive the full path of the class for its parameter. This means that just setting the string 'A' as a constructor parameter may not work in some cases.
To avoid this problem, when using ReflectionClass you will be better if you do this:
$classA = new A();
$name_classA = get_class($classA);
$ref = new ReflectionClass(get_class($name_classA));
$constName = 'MY_CONST';
echo $ref->getConstant($constName);
Function get_class will give you the full path of a class whenever you are in the code. Missing the full path may result in a "Class not found" PHP error.
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