Function is_matrix

inst/include/Rcpp/api/meat/is.h:29–32

    inline bool is_atomic(SEXP x) { return Rf_length(x) == 1; }
    inline bool is_matrix(SEXP x) {
        SEXP dim = Rf_getAttrib( x, R_DimSymbol);
        return dim != R_NilValue && Rf_length(dim) == 2;
    }
    template <> inline bool is__simple<int>(SEXP x) {
        return is_atomic(x) && TYPEOF(x) == INTSXP;
    }