r - Make return from S3 indexing function "[" invisible -

is possible return invisible object when using s3 indexing function "[" on custom class? example, in code below, there way make last line of code not print anything?

mat <- function(x) {   structure(x, class="mat") }  "[.mat" <- function(x, i, j) {   invisible(unclass(x)[i,j]) }  m1 <- mat(matrix(1:10, ncol=2)) m1[1:2,]       [,1] [,2] [1,]    1    6 [2,]    2    7 

the problem value returned [.mat not of class mat since you're using unclass, uses default printing method whatever class has. fix this, ensure returned object still mat , define printing method mat objects.

mat <- function(x) {     class(x) <- "mat"     x }  `[.mat` <- function(x, i, j) {     y <- mat(unclass(x)[i, j])     invisible(y) }  print.mat <- function(x, ...) {     invisible(x) }  test <- mat(matrix(1:10, ncol = 2))  test[1, 1] # nothing printed