Some methods for a history stack data structure. It can store history of certain repeating actions. For example, building the back-end of a file/image editor, allow undo/redo actions.
an R6 class object
If the stack reaches the limit and you are trying to add more history, the first history step will be removed , all history will be shift to the left by one step and finally add the new step to the end.
When history returning methods are called, like the get(), forward(), backward()
methods, it will not directly return the item saved, but a list, contains 4
components: 1. item, the actual item stored; 2. pos, current posistion value;
3. first, boolean value, if this history is stored on the first position of stack;
4. last, boolean value, if this history is stored on the last position of stack;
If you forward beyond last step, or backward to prior the first
step, it will be stopped with errors.
Starting history stack with no initial history will return a special
stack, where the pos = 0, len = 0, first = TRUE, and last = TRUE.
This means you cannot move forward or backward. When you get(), it will be
an empty list list(). After adding any new history, pos will never be
0 again, it will always be a larger than 0 value.
new()create the history object
historyStack$new(items = NULL, limit = 25, verbose = TRUE)
itemslist, initial history step items to store on start
limitint, how many history steps can be stored in the stack, default 25 steps
verbosebool, print some verbose message?
clear()clear all history steps in the stack
historyStack$clear()
get()retrieve the history from a certain position in the stack
historyStack$get(pos = private$pos)
posint, which position to get the history from, default is current step.
getPos()get current step position in the history stack
historyStack$getPos()
status()print out some status of the stack
historyStack$status()
returns a list of pos: current position (int); len: current
length of the history stack (int); limit: history stack storing limit (int);
first: is current step position the first of the stack (bool);
last: is current step position the last of the stack (bool)
forward()move one step forward in the history stack and return item in that position
historyStack$forward()
backward()move one step backward in the history stack and return item in that position
historyStack$backward()
add()Add an item to the history and move one step forward
historyStack$add(item)
itemany object you want to add to the stack. Everything store in the item will be moved into a list, so even if item may be something length > 1, it will still be treated as a single item and single history step.
If current position is not the last position, and when a new step item is added to the stack, all history records (items) after current position will be removed before adding the new history item.
clone()The objects of this class are cloneable with this method.
historyStack$clone(deep = FALSE)
deepWhether to make a deep clone.
his <- historyStack$new() #> Created a history stack which can record 25 steps # add some history his$add(1) #> Added one item to position 1 his$add(2) #> Added one item to position 2 his$add(3) #> Added one item to position 3 his$add(4) #> Added one item to position 4 his$add(5) #> Added one item to position 5 # check status his$status() #> $pos #> [1] 5 #> #> $len #> [1] 5 #> #> $limit #> [1] 25 #> #> $first #> [1] FALSE #> #> $last #> [1] TRUE #> # get item at current history position his$get() #> $item #> [1] 5 #> #> $pos #> [1] 5 #> #> $first #> [1] FALSE #> #> $last #> [1] TRUE #> # go back to previous step his$backward() #> $item #> [1] 4 #> #> $pos #> [1] 4 #> #> $first #> [1] FALSE #> #> $last #> [1] FALSE #> # going back to step 2 his$backward() #> $item #> [1] 3 #> #> $pos #> [1] 3 #> #> $first #> [1] FALSE #> #> $last #> [1] FALSE #> his$backward() #> $item #> [1] 2 #> #> $pos #> [1] 2 #> #> $first #> [1] FALSE #> #> $last #> [1] FALSE #> # going forward 1 step tp step 3 his$forward() #> $item #> [1] 3 #> #> $pos #> [1] 3 #> #> $first #> [1] FALSE #> #> $last #> [1] FALSE #> # check current status his$status() #> $pos #> [1] 3 #> #> $len #> [1] 5 #> #> $limit #> [1] 25 #> #> $first #> [1] FALSE #> #> $last #> [1] FALSE #> # adding a new step at position 3 will remove the old step 4,5 before adding his$add("new 4") #> Added one item to position 4 # only 3 steps + 1 new step = 4 steps left his$status() #> $pos #> [1] 4 #> #> $len #> [1] 4 #> #> $limit #> [1] 25 #> #> $first #> [1] FALSE #> #> $last #> [1] TRUE #>