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