template isValidOperator(L, string op, R)
static if(!(op != "="))
static if((isMatrix!L || isAbstractMatrix!L) && (isMatrix!R || isAbstractMatrix!R))
enum isValidOperator =
isAssignable!(typeof(L.init.at(0, 0)), typeof(R.init.at(0, 0))) && isValidOperatorImpl!(L, "+", R);