R6 classes without the repetition

example.r

r6_class(
    MyClass,
    {
        initialize = function (x) {
            private$x = x
        }

        get = function () private$x
    },
    private = {
        x = NULL
    }
)

MyClass(x = 42)$get()
# [1] 42

r6_class.r

r6_class = function (name, public = {}, private = {}, ...) {
    block_to_named = function (block) {
        is_assign = function (expr) {
            is.call(expr) && as.character(expr[[1L]]) %in% c("=", "<-")
        }

        stopifnot(identical(block[[1L]], quote(`{`)))
        block = block[-1L]
        stopifnot(all(vapply(block, is_assign, logical(1L))))

        names = lapply(block, `[[`, 2L)
        values = lapply(lapply(block, `[[`, 3L), eval, envir = caller)
        setNames(values, names)
    }

    caller = parent.frame()

    stopifnot(is.name(substitute(name)))
    name = deparse1(substitute(name))
    dots = match.call(expand.dots = FALSE)$...
    dots$public = block_to_named(substitute(public))
    dots$private = block_to_named(substitute(private))

    impl = do.call(R6::R6Class, c(name, dots))
    assign(name, impl$new, envir = caller)
}