Cannot access class attributes directly

[cdaily@…]

I ran across this bug after creating a layer and adding points to it using
addFeature() and then attempting to use queryByPoint() to find the nearest point
from that layer.

The problem is that, without a shapefile, no index value is set for each point
shape.  When getResult is called on the layer after queryByPoint, shapeindex and
tileindex are both -1, and the getShape call chokes.

Solutions to this problem that I'd found online involved setting the
$shape->index value manually, but those solutions were in perl.  That wouldn't
work in PHP, as index is 'read only'.

For my purposes I adjusted the shape->set() in php_mapscript.c to allow the
setting of the index attribute, and now everything works great.  But I'm curious
as to why all of the attributes are not directly accessible.  In particular, I
can't find a way to set the 'values' attribute.  In perl, it appears that these
attributes are all directly accessible to mapscript.