R/methods_peek.R

In datastructures: Implementation of Core Data Structures

# datastructures: Implementation of core datastructures for R.
#
# Copyright (C) Simon Dirmeier
#
# This file is part of datastructures.
#
# datastructures is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# datastructures is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with datastructures. If not, see <http://www.gnu.org/licenses/>.


#' @title Have a look at the first element from an object without removing it
#'
#' @description Peeks into an object, i.e. takes the first element and returns
#'  it without removing it from the object. The data structure that has a peek
#'  method usually uses some sort of priority of its elements.
#'
#' @export
#' @docType methods
#' @rdname peek-methods
#'
#' @param obj  the object to peek
#'
#' @return  returns the first element from \code{obj} as list
#'
#' @examples
#'
#' # peeks into a queue
#' q <- queue()
#' q <- insert(q, list(environment(), data.frame(a = 1)))
#' peek(q)
#'
#' # peeks into a fibonacci heap
#' b_heap <- binomial_heap()
#' b_heap <- insert(b_heap, letters[seq(3)], list(1, diag(3), rnorm(2)))
#' peek(b_heap)
#'
#' # peeks into a \code{hashmap}
#' h_map <- hashmap()
#' h_map[letters] <- rnorm(length(letters))
#' peek(h_map)
#'
#' # peeks into a \code{bimap}
#' b_map <- bimap("integer", "integer")
#' b_map[seq(10)] <- seq(10, 1)
#' peek(b_map)
setGeneric(
  "peek",
  function(obj) {
    standardGeneric("peek")
  },
  package = "datastructures"
)