oop - php class constants with bitvalues

Can classes have bitshifted values defined as class constants / static variables ?

I want to implement a permission system similar to the one described here http://www.litfuel.net/tutorials/bitwise.htm (sorry best example I could find from a quick google)

For example ive tried this

class permissions {
const perm1 =1;
const perm2 =2;
const perm3 =4;
//--CUT--
const perm24 =8388608;


const perm25 = perm1 | perm2;

}

which gives

syntax error, unexpected '|', expecting ',' or ';'

and the preferred way

class permissions {
static $perm1 =1<<0;
static $perm2 =1<<1;
static $perm3 =1<<2;
//--CUT--
static $perm24 =1<<23;

static $perm25 = $perm1 | $perm2;

}  

which gives

syntax error, unexpected T_SL, expecting ',' or ';'

The latter way works outside of a class environment eg

$perm1 =1<<0;
$perm2 =1<<1;
$perm3 =1<<2;
//--CUT--
$perm24 =1<<23;

$perm25 = $perm1 | $perm2;
echo $perm25;

Giving the expected 3 (2+1) (or 2^0 + 2^1)

What is the best way to define this in a class ?

Answer

Quoting from the docs:

The value must be a constant expression, not (for example) a variable, a property, a result of a mathematical operation, or a function call.

bitwise or logical operations qualify (like mathematical operations) as not permitted