在另一个数组元素中包含数组元素值？

Is it possible to have an array assign its own element value to one of its other elements at the time you declare the array?

Here's a code example:

$arr = array ( 0 => '<ul class="'.$arr[1].'">', 1 => 'some_class' );

echo $arr[0]; // <ul class="some_class">

I've tried passing by reference (&$arr[1] instead of $arr[1] in the above code), but it gives a syntax error.

You can do something along these lines

$arr = array ( '<ul class="%s">', 'some_class' );

and when you want to render just call

echo call_user_func_array("sprintf", $arr);

No, you can't access an element of an array before the array has been declared. Just use another variable:

$class_name = 'some_class'
$arr = array ( 0 => '<ul class="'.$class_name.'">', 1 => $class_name );

echo $arr[0]; // <ul class="some_class">

You could also assign elements individually and refer to them in later assignments:

$arr = array();
$arr[1] = 'some_class';
$arr[0] = '<ul class="'.$arr[1].'">';

echo $arr[0]; // <ul class="some_class">