John:Mass!(T,S) opAdd(Mass!(T,S) other) {If you are using D2 then don't use opAdd, use opBinary: http://dlang.org/operatoroverloading.html#Binary
Time ago I added an enhancement request for a warning (that later is meant to become a deprecation) that helps avoid your problem:
http://d.puremagic.com/issues/show_bug.cgi?id=10320 Bye, bearophile
