diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 38080dd90..d575d5dd7 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,9 +1,9 @@
 # All available hooks: https://pre-commit.com/hooks.html
 repos:
 -   repo: https://github.com/lorenzwalthert/precommit
-    rev: v0.0.0.9018
+    rev: v0.0.0.9024
     hooks:
-    -   id: lintr
+    # -   id: lintr
     -   id: parsable-R
     -   id: no-browser-statement
     -   id: readme-rmd-rendered
diff --git a/.travis.yml b/.travis.yml
index 68273b8ea..b807f9d6e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,7 @@
 # Usually you shouldn't need to change the first part of the file
 
 # DO NOT CHANGE THE CODE BELOW
-before_install: R -q -e 'install.packages(c("remotes", "curl", "knitr", "rmarkdown")); remotes::install_github("ropenscilabs/tic"); tic::prepare_all_stages(); remotes::install_deps(dependencies = TRUE); tic::before_install()'
+before_install: R -q -e 'install.packages(c("remotes", "curl", "knitr", "rmarkdown")); remotes::install_github("ropenscilabs/tic"); tic::prepare_all_stages(); remotes::install_deps(dependencies = TRUE); if (isTRUE(as.logical(toupper(Sys.getenv("R_REMOVE_RCACHE"))))) remove.packages("R.cache"); tic::before_install()'
 install: R -q -e 'tic::install()'
 after_install: R -q -e 'tic::after_install()'
 before_script: R -q -e 'tic::before_script()'
@@ -38,6 +38,9 @@ matrix:
   - r: release
     env:
     - BUILD_PKGDOWN: true
+  - r: release
+    env:
+    - R_REMOVE_RCACHE: true
   - r: devel
 
 #env
diff --git a/API b/API
index 072513601..eb4538efb 100644
--- a/API
+++ b/API
@@ -2,6 +2,10 @@
 
 ## Exported functions
 
+cache_activate(cache_name = NULL, verbose = TRUE)
+cache_clear(cache_name = NULL, ask = TRUE)
+cache_deactivate(verbose = TRUE)
+cache_info(cache_name = NULL, format = "both")
 create_style_guide(initialize = default_style_guide_attributes, line_break = NULL, space = NULL, token = NULL, indention = NULL, use_raw_indention = FALSE, reindention = tidyverse_reindention())
 default_style_guide_attributes(pd_flat)
 specify_math_token_spacing(zero = "'^'", one = c("'+'", "'-'", "'*'", "'/'"))
diff --git a/DESCRIPTION b/DESCRIPTION
index 36ca1f1be..e232a33a1 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,5 +1,5 @@
-Package: styler
 Type: Package
+Package: styler
 Title: Non-Invasive Pretty Printing of R Code
 Version: 1.2.0.9000
 Authors@R: 
@@ -30,14 +30,17 @@ Imports:
     xfun (>= 0.1)
 Suggests: 
     data.tree (>= 0.1.6),
+    digest,
     dplyr,
     here,
     knitr,
     prettycode,
+    R.cache (>= 0.14.0),
     rmarkdown,
     rstudioapi (>= 0.7),
     testthat (>= 2.1.0)
-VignetteBuilder: knitr
+VignetteBuilder: 
+    knitr
 Encoding: UTF-8
 LazyData: true
 Roxygen: list(markdown = TRUE, roclets = c("rd", "namespace",
@@ -80,8 +83,10 @@ Collate:
     'token-create.R'
     'transform-code.R'
     'transform-files.R'
-    'ui.R'
+    'ui-caching.R'
+    'ui-styling.R'
     'unindent.R'
+    'utils-cache.R'
     'utils-files.R'
     'utils-navigate-nest.R'
     'utils-strings.R'
diff --git a/NAMESPACE b/NAMESPACE
index 493c57dd1..67f3fcd43 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -1,6 +1,10 @@
 # Generated by roxygen2: do not edit by hand
 
 S3method(print,vertical)
+export(cache_activate)
+export(cache_clear)
+export(cache_deactivate)
+export(cache_info)
 export(create_style_guide)
 export(default_style_guide_attributes)
 export(specify_math_token_spacing)
diff --git a/NEWS.md b/NEWS.md
index df41e6a26..d93cba602 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -20,9 +20,16 @@
 
 ## New features
 
-* Aligned function calls are detected and kept as is if they match the styler 
-  [definition for aligned function calls](https://styler.r-lib.org/articles/detect-alignment.html)
-  (#537).
+* styler caches results of styling, so applying styler to code it has styled
+  before will be instantaneous. This brings large speed boosts in many
+  situations, e.g. when `style_pkg()` is run but only a few files have changed
+  since the last styling or when using the [styler pre-commit
+  hook](https://github.com/lorenzwalthert/pre-commit-hooks). See the README for
+  details (#538).
+
+* Aligned function calls are detected and remain unchanged if they match the styler
+  [definition for aligned function
+  calls](https://styler.r-lib.org/articles/detect-alignment.html) (#537).
 
 * curly-curly (`{{`) syntactic sugar introduced with rlang 0.4.0 is now 
   explicitly handled, where previously it was just treated as two consecutive 
diff --git a/R/addins.R b/R/addins.R
index 367b9ce9e..aa2a38157 100644
--- a/R/addins.R
+++ b/R/addins.R
@@ -141,7 +141,7 @@ set_style_transformers <- function() {
 #'
 #' @keywords internal
 get_addins_style_transformer_name <- function() {
-  getOption("styler.addins_style_transformer", default = "styler::tidyverse_style()")
+  getOption("styler.addins_style_transformer")
 }
 
 #' @rdname get_addins_style_transformer_name
diff --git a/R/communicate.R b/R/communicate.R
index 3e9328b8a..344673f99 100644
--- a/R/communicate.R
+++ b/R/communicate.R
@@ -34,3 +34,37 @@ assert_data.tree_installation <- function() {
     abort("The package data.tree needs to be installed for this functionality.")
   }
 }
+
+#' Assert the R.cache installation in conjunction with the cache config
+#'
+#' R.cache needs to be installed if caching functionality is enabled
+#' @param installation_only Whether or not to only check if R.cache is
+#'   installed.
+#' @keywords internal
+assert_R.cache_installation <- function(installation_only = FALSE,
+                                        action = "abort") {
+  # fail if R.cache is not installed but feature is actiavted.
+  if (!rlang::is_installed("R.cache") &&
+    ifelse(installation_only, TRUE, cache_is_activated())
+  ) {
+    msg_basic <- paste(
+      "R package R.cache is not installed, which is needed when the caching ",
+      "feature is activated. Please install the package with ",
+      "`install.packages('R.cache')` and then restart R to enable the ",
+      "caching feature of styler or permanently deactivate the feature by ",
+      "adding `styler::cache_deactivate()` to your .Rprofile, e.g. via ",
+      "`usethis::edit_r_profile()`.",
+      sep = ""
+    )
+
+    if (action == "abort") {
+      rlang::abort(msg_basic)
+    } else {
+      rlang::warn(paste0(
+        msg_basic, " ",
+        "Deactivating the caching feature for the current session."
+      ))
+      cache_deactivate(verbose = FALSE)
+    }
+  }
+}
diff --git a/R/io.R b/R/io.R
index 8b9ed49b4..385b4ce91 100644
--- a/R/io.R
+++ b/R/io.R
@@ -61,7 +61,7 @@ read_utf8 <- function(path) {
   }
 }
 
-#' Drop-in replacement for [xfun::read_utf8()], with an optional `warn`
+#' Drop-in replacement for `xfun::read_utf8()`, with an optional `warn`
 #' argument.
 #' @keywords internal
 read_utf8_bare <- function(con, warn = TRUE) {
@@ -80,7 +80,7 @@ read_utf8_bare <- function(con, warn = TRUE) {
   x
 }
 
-#' Drop-in replacement for `xfun:::invalid_utf8()`.
+#' Drop-in replacement for [xfun:::invalid_utf8()]
 #' @keywords internal
 invalid_utf8 <- function(x) {
   which(!is.na(x) & is.na(iconv(x, "UTF-8", "UTF-8")))
diff --git a/R/roxygen-examples-parse.R b/R/roxygen-examples-parse.R
index 3d3d6ff77..3d923d384 100644
--- a/R/roxygen-examples-parse.R
+++ b/R/roxygen-examples-parse.R
@@ -33,8 +33,7 @@ parse_roxygen <- function(roxygen) {
 #' @param raw Raw code to post-process.
 #' @keywords internal
 post_parse_roxygen <- function(raw) {
-  split <- raw %>%
+  raw %>%
     paste0(collapse = "") %>%
-    strsplit("\n", fixed = TRUE)
-  split[[1]]
+    convert_newlines_to_linebreaks()
 }
diff --git a/R/serialize.R b/R/serialize.R
index 6857563b4..810825d7a 100644
--- a/R/serialize.R
+++ b/R/serialize.R
@@ -14,5 +14,5 @@ serialize_parse_data_flattened <- function(flattened_pd, start_line = 1) {
       map(lag_newlines, add_newlines), map(lag_spaces, add_spaces), text
     )
   )
-  strsplit(res, "\n")[[1L]]
+  convert_newlines_to_linebreaks(res)
 }
diff --git a/R/transform-files.R b/R/transform-files.R
index f4749a285..bda9803c6 100644
--- a/R/transform-files.R
+++ b/R/transform-files.R
@@ -73,17 +73,47 @@ transform_file <- function(path,
 #' @inheritParams parse_transform_serialize_r
 #' @keywords internal
 #' @importFrom purrr when
-make_transformer <- function(transformers, include_roxygen_examples, warn_empty = TRUE) {
+make_transformer <- function(transformers,
+                             include_roxygen_examples,
+                             warn_empty = TRUE) {
   force(transformers)
+  cache_dir <- c("styler", cache_get_name())
+  assert_R.cache_installation(action = "warn")
+
+  is_R.cache_installed <- rlang::is_installed("R.cache")
+
   function(text) {
-    transformed_code <- text %>%
-      parse_transform_serialize_r(transformers, warn_empty = warn_empty) %>%
-      when(
-        include_roxygen_examples ~
-        parse_transform_serialize_roxygen(., transformers),
-        ~.
-      )
-    transformed_code
+    should_use_cache <- is_R.cache_installed && cache_is_activated()
+
+    if (should_use_cache) {
+      use_cache <- R.cache::generateCache(
+        key = cache_make_key(text, transformers),
+        dirs = cache_dir
+      ) %>%
+        file.exists()
+    } else {
+      use_cache <- FALSE
+    }
+
+    if (!use_cache) {
+      transformed_code <- text %>%
+        parse_transform_serialize_r(transformers, warn_empty = warn_empty) %>%
+        when(
+          include_roxygen_examples ~
+          parse_transform_serialize_roxygen(., transformers),
+          ~.
+        )
+      if (should_use_cache) {
+        R.cache::generateCache(
+          key = cache_make_key(transformed_code, transformers),
+          dirs = cache_dir
+        ) %>%
+          file.create()
+      }
+      transformed_code
+    } else {
+      text
+    }
   }
 }
 
diff --git a/R/ui-caching.R b/R/ui-caching.R
new file mode 100644
index 000000000..4d3fd9ce5
--- /dev/null
+++ b/R/ui-caching.R
@@ -0,0 +1,105 @@
+#' Clear the cache
+#'
+#' Clears the cache that stores which files are already styled. You won't be
+#' able to undo this. Note that the file corresponding to the cache (a folder
+#' on your file stystem) won't be deleted, but it will be empty after calling
+#' `cache_clear`.
+#' @param cache_name The name of the styler cache to use. If
+#'   `NULL`, the option "styler.cache_name" is considered which defaults to
+#'   the version of styler used.
+#' @details
+#' Each version of styler has it's own cache by default, because styling is
+#' potentially different with different versions of styler.
+#' @param ask Whether or not to interactively ask the user again.
+#' @family cache managers
+#' @export
+cache_clear <- function(cache_name = NULL, ask = TRUE) {
+  assert_R.cache_installation(installation_only = TRUE)
+  path_cache <- cache_find_path(cache_name)
+  R.cache::clearCache(path_cache, prompt = ask)
+  cache_deactivate(verbose = FALSE)
+}
+
+#' Show information about the styler cache
+#'
+#' Gives information about the cache. Note that the size consumed by the cache
+#' will always be displayed as zero because all the cache does is creating an
+#' empty file of size 0 bytes for every cached expression. The innode is
+#' excluded from this displayed size but negligible.
+#' @param cache_name The name of the cache for which to show details. If
+#'   `NULL`, the active cache is used. If none is active the cache corresponding
+#'   to the installed styler version is used.
+#' @param format Either "lucid" for a summary emitted with [base::cat()],
+#'   "tabular" for a tabular summary from [base::file.info()] or "both" for
+#'   both.
+#' @family cache managers
+#' @export
+cache_info <- function(cache_name = NULL, format = "both") {
+  assert_R.cache_installation(installation_only = TRUE)
+  rlang::arg_match(format, c("tabular", "lucid", "both"))
+  path_cache <- cache_find_path(cache_name)
+  files <- list.files(path_cache, full.names = TRUE)
+  file_info <- file.info(files) %>%
+    as_tibble()
+  tbl <- tibble(
+    n = nrow(file_info),
+    size = sum(file_info$size),
+    last_modified = suppressWarnings(max(file_info$mtime)),
+    created = file.info(path_cache)$ctime,
+    location = path_cache,
+    activated = cache_is_activated(cache_name)
+  )
+  if (format %in% c("lucid", "both")) {
+    cat(
+      "Size:\t\t", tbl$size, " bytes (", tbl$n, " cached expressions)",
+      "\nLast modified:\t", as.character(tbl$last_modified),
+      "\nCreated:\t", as.character(tbl$created),
+      "\nLocation:\t", path_cache,
+      "\nActivated:\t", tbl$activated,
+      "\n",
+      sep = ""
+    )
+  }
+  if (format == "tabular") {
+    tbl
+  } else if (format == "both") {
+    invisible(tbl)
+  }
+}
+
+#' Activate or deactivate the styler cache
+#'
+#' Helper functions to control the behavior of caching. Simple wrappers around
+#' [base::options()].
+#' @inheritParams cache_clear
+#' @param verbose Whether or not to print an informative message about what the
+#'   function is doing.
+#' @family cache managers
+#' @export
+cache_activate <- function(cache_name = NULL, verbose = TRUE) {
+  assert_R.cache_installation(installation_only = TRUE)
+  if (!is.null(cache_name)) {
+    options("styler.cache_name" = cache_name)
+  } else {
+    options("styler.cache_name" = styler_version)
+  }
+  path <- cache_find_path(cache_name)
+  if (verbose) {
+    cat(
+      "Using cache ", cache_get_name(), " at ",
+      path, ".\n",
+      sep = ""
+    )
+  }
+  invisible(path)
+}
+
+#' @rdname cache_activate
+#' @export
+cache_deactivate <- function(verbose = TRUE) {
+  options("styler.cache_name" = NULL)
+
+  if (verbose) {
+    cat("Deactivated cache.\n")
+  }
+}
diff --git a/R/ui.R b/R/ui-styling.R
similarity index 100%
rename from R/ui.R
rename to R/ui-styling.R
diff --git a/R/utils-cache.R b/R/utils-cache.R
new file mode 100644
index 000000000..f97486013
--- /dev/null
+++ b/R/utils-cache.R
@@ -0,0 +1,112 @@
+#' Standardize text for hashing
+#'
+#' Make sure text after styling results in the same hash as text before styling
+#' if it is indeed identical.
+#' @param text A character vector.
+#' @keywords internal
+hash_standardize <- function(text) {
+  text %>%
+    convert_newlines_to_linebreaks() %>%
+    ensure_last_is_empty() %>%
+    enc2utf8() %>%
+    paste0(collapse = "\n") %>%
+    list()
+}
+
+#' Make a key for `R.cache`
+#'
+#' @details
+#'
+#' This function standardizes text and converts transformers to character (to
+#' avoid issues described in details).
+#' This means that the same code in `transformers`,
+#' calling other code not in `transformers` that was modified, will lead
+#' styler into thinking we can use the cache, although we should not. We believe
+#' this is a highly unlikely event, in particular because we already invalidate
+#' the cache when the styler version changes. Hence, our cache will cause
+#' styler to return *not correctly styled* code iff one of these conditions
+#' holds:
+#' - An improperly versioned version of styler is used, e.g. the development
+#'   version on GitHub.
+#' - A style guide from outside styler is used.
+#'
+#' Plus for both cases: the code in transformers does not change and changes in
+#' code the transformers depend on result in different styling.
+#' @section Experiments:
+#'
+#' There is unexamplainable behavior in conjunction with hashin and
+#' environments:
+#' * Functions created with `purrr::partial()` are not identical when compared
+#'   with `identical()`
+#'   ([StackOverflow](https://stackoverflow.com/questions/58656033/when-are-purrrpartial-ized-functions-identical))
+#' * except when they have the exact same parent environment, which must be an
+#'   object created and then passed to `purrr::partial(.env = ...)`, not
+#'   created in-place.
+#' * `purrr::partial()` seems to ignore `.env` after version 0.2.5, so until
+#'   this is fixed, we'd have to work with version 0.2.5.
+#' * Our caching backend package, `R.cache`, uses
+#'   `R.cache:::getChecksum.default` (which uses `digest::digest()`) to hash the
+#'   input. The latter does not seem to care if the environments are exactly
+#'   equal (see 'Exampels').
+#' * However, under stome circumstances, it does: Commit 9c94c022 (if not
+#'   overwritten / rebased by now) contains a reprex. Otherwise, search for
+#'   43219ixmypi in commit messages and restore this commit to reproduce the
+#'   behavior.
+#' @examples
+#' add <- function(x, y) {
+#' x + y
+#' }
+#' add1 <- purrr::partial(add, x = 1)
+#' add2 <- purrr::partial(add, x = 1)
+#' identical(add1, add2)
+#' identical(digest::digest(add1), digest::digest(add2))
+#' identical(digest::digest(styler::tidyverse_style()), digest::digest(styler::tidyverse_style()))
+#' @keywords internal
+cache_make_key <- function(text, transformers) {
+  text <- hash_standardize(text)
+  c(text = text, transformers = as.character(transformers))
+}
+
+#' Where is the cache?
+#'
+#' Finds the path to the cache and creates it if it does not exist.
+#' @inheritParams cache_clear
+#' @keywords internal
+cache_find_path <- function(cache_name = NULL) {
+  cache_name <- cache_get_or_derive_name(cache_name)
+  R.cache::getCachePath(c("styler", cache_name))
+}
+
+#' Check if a cache is activated
+#'
+#' @param cache_name The name of the cache to check. If `NULL`, we check if
+#'   any cache is activated. If not `NULL`, we check if a specific cache is
+#'   activated.
+#' @keywords internal
+cache_is_activated <- function(cache_name = NULL) {
+  current_cache <- cache_get_name()
+  if (is.null(cache_name)) {
+    !is.null(current_cache)
+  } else if (!is.null(current_cache)) {
+    cache_name == current_cache
+  } else {
+    FALSE
+  }
+}
+
+styler_version <- unlist(unname(read.dcf("DESCRIPTION")[, "Version"]))
+
+cache_get_name <- function() {
+  getOption("styler.cache_name")
+}
+
+cache_get_or_derive_name <- function(cache_name) {
+  if (is.null(cache_name)) {
+    cache_name <- cache_get_name()
+    if (is.null(cache_name)) {
+      cache_name <- styler_version
+    }
+  }
+  cache_name
+}
+
diff --git a/R/utils.R b/R/utils.R
index 3aa6aef91..d532c0614 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -4,13 +4,39 @@ line_col_names <- function() {
   c("line1", "line2", "col1", "col2")
 }
 
+#' Ensure there is one (and only one) blank line at the end of a vector
+#' @examples
+#' styler:::ensure_last_is_empty("")
+#' styler:::ensure_last_is_empty(letters)
+#' styler:::ensure_last_is_empty(c(letters, "", "", ""))
+#' @keywords internal
 ensure_last_is_empty <- function(x) {
-  has_line_break_at_eof <- x[length(x)] == ""
-  if (has_line_break_at_eof) {
-    return(x)
-  } else {
-    append(x, "")
+  if (all(x == "")) {
+    return("")
   }
+  x <- c(x, "", "")
+  x <- x[seq(1, length(x) - which(rev(x) != "")[1] + 2L)]
+  x
+}
+
+#' Replace the newline character with a line break
+#'
+#' @param text A character vector
+#' @examples
+#' styler:::convert_newlines_to_linebreaks("x\n2")
+#' # a simple strsplit approach does not cover both cases
+#' unlist(strsplit("x\n\n2", "\n", fixed = TRUE))
+#' unlist(strsplit(c("x", "", "2"), "\n", fixed = TRUE))
+#' styler:::convert_newlines_to_linebreaks(c("x", "2"))
+#' @keywords internal
+convert_newlines_to_linebreaks <- function(text) {
+  split <- strsplit(text, "\n", fixed = TRUE)
+  map(split, ~ if (identical(.x, character(0))) {
+    ""
+    } else {
+      .x
+    }) %>%
+    unlist()
 }
 
 #' Check whether two columns match
diff --git a/R/zzz.R b/R/zzz.R
index 59f5a93e2..3094409b9 100644
--- a/R/zzz.R
+++ b/R/zzz.R
@@ -3,6 +3,8 @@
   op <- options()
   op.styler <- list(
     styler.colored_print.vertical = TRUE,
+    styler.cache_name = styler_version,
+    styler.addins_style_transformer = "styler::tidyverse_style()",
     styler.ignore_start = "# styler: off",
     styler.ignore_stop = "# styler: on"
   )
diff --git a/README.Rmd b/README.Rmd
index 9f19bd2da..f66a748f7 100644
--- a/README.Rmd
+++ b/README.Rmd
@@ -129,6 +129,17 @@ is not flexible enough for you, you can implement your own style guide, as
 explained in the corresponding
 [vignette](https://styler.r-lib.org/articles/customizing_styler.html).
 
+**caching**
+
+In styler 1.1.1,9004, caching was introduced, which makes repeated styling
+almost instantaneous. By default, it's enabled, but you need to have the
+`R.cache` package installed. At first use, `R.cache` will ask you to let it
+create a permanent cache on your file system that styler will use. This is needed
+if you want to cache across R sessions and not just within. The cache is
+specific to a version of styler by default, because different versions
+potentially format code differently. See `?styler::cache_info()` for more
+details on how to configure caching.
+
 ## Adaption of styler
 
 styler functionality is made available through other tools, most notably
diff --git a/README.md b/README.md
index 7a546759e..58021b973 100644
--- a/README.md
+++ b/README.md
@@ -125,6 +125,17 @@ If this is not flexible enough for you, you can implement your own style
 guide, as explained in the corresponding
 [vignette](https://styler.r-lib.org/articles/customizing_styler.html).
 
+**caching**
+
+In styler 1.1.1,9004, caching was introduced, which makes repeated
+styling almost instantaneous. By default, it’s enabled, but you need to
+have the `R.cache` package installed. At first use, `R.cache` will ask
+you to let it create a permanent cache on your file system that styler
+will use. This is needed if you want to cache across R sessions and not
+just within. The cache is specific to a version of styler by default,
+because different versions potentially format code differently. See
+`?styler::cache_info()` for more details on how to configure caching.
+
 ## Adaption of styler
 
 styler functionality is made available through other tools, most notably
diff --git a/man/assert_R.cache_installation.Rd b/man/assert_R.cache_installation.Rd
new file mode 100644
index 000000000..61f812c95
--- /dev/null
+++ b/man/assert_R.cache_installation.Rd
@@ -0,0 +1,16 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/communicate.R
+\name{assert_R.cache_installation}
+\alias{assert_R.cache_installation}
+\title{Assert the R.cache installation in conjunction with the cache config}
+\usage{
+assert_R.cache_installation(installation_only = FALSE, action = "abort")
+}
+\arguments{
+\item{installation_only}{Whether or not to only check if R.cache is
+installed.}
+}
+\description{
+R.cache needs to be installed if caching functionality is enabled
+}
+\keyword{internal}
diff --git a/man/cache_activate.Rd b/man/cache_activate.Rd
new file mode 100644
index 000000000..4bdb5d921
--- /dev/null
+++ b/man/cache_activate.Rd
@@ -0,0 +1,29 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/ui-caching.R
+\name{cache_activate}
+\alias{cache_activate}
+\alias{cache_deactivate}
+\title{Activate or deactivate the styler cache}
+\usage{
+cache_activate(cache_name = NULL, verbose = TRUE)
+
+cache_deactivate(verbose = TRUE)
+}
+\arguments{
+\item{cache_name}{The name of the styler cache to use. If
+\code{NULL}, the option "styler.cache_name" is considered which defaults to
+the version of styler used.}
+
+\item{verbose}{Whether or not to print an informative message about what the
+function is doing.}
+}
+\description{
+Helper functions to control the behavior of caching. Simple wrappers around
+\code{\link[base:options]{base::options()}}.
+}
+\seealso{
+Other cache managers: 
+\code{\link{cache_clear}()},
+\code{\link{cache_info}()}
+}
+\concept{cache managers}
diff --git a/man/cache_clear.Rd b/man/cache_clear.Rd
new file mode 100644
index 000000000..c9adb9797
--- /dev/null
+++ b/man/cache_clear.Rd
@@ -0,0 +1,31 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/ui-caching.R
+\name{cache_clear}
+\alias{cache_clear}
+\title{Clear the cache}
+\usage{
+cache_clear(cache_name = NULL, ask = TRUE)
+}
+\arguments{
+\item{cache_name}{The name of the styler cache to use. If
+\code{NULL}, the option "styler.cache_name" is considered which defaults to
+the version of styler used.}
+
+\item{ask}{Whether or not to interactively ask the user again.}
+}
+\description{
+Clears the cache that stores which files are already styled. You won't be
+able to undo this. Note that the file corresponding to the cache (a folder
+on your file stystem) won't be deleted, but it will be empty after calling
+\code{cache_clear}.
+}
+\details{
+Each version of styler has it's own cache by default, because styling is
+potentially different with different versions of styler.
+}
+\seealso{
+Other cache managers: 
+\code{\link{cache_activate}()},
+\code{\link{cache_info}()}
+}
+\concept{cache managers}
diff --git a/man/cache_find_path.Rd b/man/cache_find_path.Rd
new file mode 100644
index 000000000..3d7d0c673
--- /dev/null
+++ b/man/cache_find_path.Rd
@@ -0,0 +1,17 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils-cache.R
+\name{cache_find_path}
+\alias{cache_find_path}
+\title{Where is the cache?}
+\usage{
+cache_find_path(cache_name = NULL)
+}
+\arguments{
+\item{cache_name}{The name of the styler cache to use. If
+\code{NULL}, the option "styler.cache_name" is considered which defaults to
+the version of styler used.}
+}
+\description{
+Finds the path to the cache and creates it if it does not exist.
+}
+\keyword{internal}
diff --git a/man/cache_info.Rd b/man/cache_info.Rd
new file mode 100644
index 000000000..13f702071
--- /dev/null
+++ b/man/cache_info.Rd
@@ -0,0 +1,29 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/ui-caching.R
+\name{cache_info}
+\alias{cache_info}
+\title{Show information about the styler cache}
+\usage{
+cache_info(cache_name = NULL, format = "both")
+}
+\arguments{
+\item{cache_name}{The name of the cache for which to show details. If
+\code{NULL}, the active cache is used. If none is active the cache corresponding
+to the installed styler version is used.}
+
+\item{format}{Either "lucid" for a summary emitted with \code{\link[base:cat]{base::cat()}},
+"tabular" for a tabular summary from \code{\link[base:file.info]{base::file.info()}} or "both" for
+both.}
+}
+\description{
+Gives information about the cache. Note that the size consumed by the cache
+will always be displayed as zero because all the cache does is creating an
+empty file of size 0 bytes for every cached expression. The innode is
+excluded from this displayed size but negligible.
+}
+\seealso{
+Other cache managers: 
+\code{\link{cache_activate}()},
+\code{\link{cache_clear}()}
+}
+\concept{cache managers}
diff --git a/man/cache_is_activated.Rd b/man/cache_is_activated.Rd
new file mode 100644
index 000000000..ca3031b78
--- /dev/null
+++ b/man/cache_is_activated.Rd
@@ -0,0 +1,17 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils-cache.R
+\name{cache_is_activated}
+\alias{cache_is_activated}
+\title{Check if a cache is activated}
+\usage{
+cache_is_activated(cache_name = NULL)
+}
+\arguments{
+\item{cache_name}{The name of the cache to check. If \code{NULL}, we check if
+any cache is activated. If not \code{NULL}, we check if a specific cache is
+activated.}
+}
+\description{
+Check if a cache is activated
+}
+\keyword{internal}
diff --git a/man/cache_make_key.Rd b/man/cache_make_key.Rd
new file mode 100644
index 000000000..a3890ce02
--- /dev/null
+++ b/man/cache_make_key.Rd
@@ -0,0 +1,66 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils-cache.R
+\name{cache_make_key}
+\alias{cache_make_key}
+\title{Make a key for \code{R.cache}}
+\usage{
+cache_make_key(text, transformers)
+}
+\description{
+Make a key for \code{R.cache}
+}
+\details{
+This function standardizes text and converts transformers to character (to
+avoid issues described in details).
+This means that the same code in \code{transformers},
+calling other code not in \code{transformers} that was modified, will lead
+styler into thinking we can use the cache, although we should not. We believe
+this is a highly unlikely event, in particular because we already invalidate
+the cache when the styler version changes. Hence, our cache will cause
+styler to return \emph{not correctly styled} code iff one of these conditions
+holds:
+\itemize{
+\item An improperly versioned version of styler is used, e.g. the development
+version on GitHub.
+\item A style guide from outside styler is used.
+}
+
+Plus for both cases: the code in transformers does not change and changes in
+code the transformers depend on result in different styling.
+}
+\section{Experiments}{
+
+
+There is unexamplainable behavior in conjunction with hashin and
+environments:
+\itemize{
+\item Functions created with \code{purrr::partial()} are not identical when compared
+with \code{identical()}
+(\href{https://stackoverflow.com/questions/58656033/when-are-purrrpartial-ized-functions-identical}{StackOverflow})
+\item except when they have the exact same parent environment, which must be an
+object created and then passed to \code{purrr::partial(.env = ...)}, not
+created in-place.
+\item \code{purrr::partial()} seems to ignore \code{.env} after version 0.2.5, so until
+this is fixed, we'd have to work with version 0.2.5.
+\item Our caching backend package, \code{R.cache}, uses
+\code{R.cache:::getChecksum.default} (which uses \code{digest::digest()}) to hash the
+input. The latter does not seem to care if the environments are exactly
+equal (see 'Exampels').
+\item However, under stome circumstances, it does: Commit 9c94c022 (if not
+overwritten / rebased by now) contains a reprex. Otherwise, search for
+43219ixmypi in commit messages and restore this commit to reproduce the
+behavior.
+}
+}
+
+\examples{
+add <- function(x, y) {
+x + y
+}
+add1 <- purrr::partial(add, x = 1)
+add2 <- purrr::partial(add, x = 1)
+identical(add1, add2)
+identical(digest::digest(add1), digest::digest(add2))
+identical(digest::digest(styler::tidyverse_style()), digest::digest(styler::tidyverse_style()))
+}
+\keyword{internal}
diff --git a/man/convert_newlines_to_linebreaks.Rd b/man/convert_newlines_to_linebreaks.Rd
new file mode 100644
index 000000000..9ac928a95
--- /dev/null
+++ b/man/convert_newlines_to_linebreaks.Rd
@@ -0,0 +1,22 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils.R
+\name{convert_newlines_to_linebreaks}
+\alias{convert_newlines_to_linebreaks}
+\title{Replace the newline character with a line break}
+\usage{
+convert_newlines_to_linebreaks(text)
+}
+\arguments{
+\item{text}{A character vector}
+}
+\description{
+Replace the newline character with a line break
+}
+\examples{
+styler:::convert_newlines_to_linebreaks("x\n2")
+# a simple strsplit approach does not cover both cases
+unlist(strsplit("x\n\n2", "\n", fixed = TRUE))
+unlist(strsplit(c("x", "", "2"), "\n", fixed = TRUE))
+styler:::convert_newlines_to_linebreaks(c("x", "2"))
+}
+\keyword{internal}
diff --git a/man/ensure_last_is_empty.Rd b/man/ensure_last_is_empty.Rd
new file mode 100644
index 000000000..91cdd2aba
--- /dev/null
+++ b/man/ensure_last_is_empty.Rd
@@ -0,0 +1,17 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils.R
+\name{ensure_last_is_empty}
+\alias{ensure_last_is_empty}
+\title{Ensure there is one (and only one) blank line at the end of a vector}
+\usage{
+ensure_last_is_empty(x)
+}
+\description{
+Ensure there is one (and only one) blank line at the end of a vector
+}
+\examples{
+styler:::ensure_last_is_empty("")
+styler:::ensure_last_is_empty(letters)
+styler:::ensure_last_is_empty(c(letters, "", "", ""))
+}
+\keyword{internal}
diff --git a/man/hash_standardize.Rd b/man/hash_standardize.Rd
new file mode 100644
index 000000000..8f210cc1e
--- /dev/null
+++ b/man/hash_standardize.Rd
@@ -0,0 +1,16 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils-cache.R
+\name{hash_standardize}
+\alias{hash_standardize}
+\title{Standardize text for hashing}
+\usage{
+hash_standardize(text)
+}
+\arguments{
+\item{text}{A character vector.}
+}
+\description{
+Make sure text after styling results in the same hash as text before styling
+if it is indeed identical.
+}
+\keyword{internal}
diff --git a/man/invalid_utf8.Rd b/man/invalid_utf8.Rd
index 9c9479add..9b1b64e75 100644
--- a/man/invalid_utf8.Rd
+++ b/man/invalid_utf8.Rd
@@ -2,11 +2,11 @@
 % Please edit documentation in R/io.R
 \name{invalid_utf8}
 \alias{invalid_utf8}
-\title{Drop-in replacement for \code{xfun:::invalid_utf8()}.}
+\title{Drop-in replacement for \code{\link[xfun:::invalid_utf8]{xfun::::invalid_utf8()}}}
 \usage{
 invalid_utf8(x)
 }
 \description{
-Drop-in replacement for \code{xfun:::invalid_utf8()}.
+Drop-in replacement for \code{\link[xfun:::invalid_utf8]{xfun::::invalid_utf8()}}
 }
 \keyword{internal}
diff --git a/man/prettify_any.Rd b/man/prettify_any.Rd
index b85971a8b..3be33cc50 100644
--- a/man/prettify_any.Rd
+++ b/man/prettify_any.Rd
@@ -1,5 +1,5 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/ui.R
+% Please edit documentation in R/ui-styling.R
 \name{prettify_any}
 \alias{prettify_any}
 \title{Prettify R code in current working directory}
diff --git a/man/read_utf8_bare.Rd b/man/read_utf8_bare.Rd
index 725efac7f..52f397af4 100644
--- a/man/read_utf8_bare.Rd
+++ b/man/read_utf8_bare.Rd
@@ -2,13 +2,13 @@
 % Please edit documentation in R/io.R
 \name{read_utf8_bare}
 \alias{read_utf8_bare}
-\title{Drop-in replacement for \code{\link[xfun:read_utf8]{xfun::read_utf8()}}, with an optional \code{warn}
+\title{Drop-in replacement for \code{xfun::read_utf8()}, with an optional \code{warn}
 argument.}
 \usage{
 read_utf8_bare(con, warn = TRUE)
 }
 \description{
-Drop-in replacement for \code{\link[xfun:read_utf8]{xfun::read_utf8()}}, with an optional \code{warn}
+Drop-in replacement for \code{xfun::read_utf8()}, with an optional \code{warn}
 argument.
 }
 \keyword{internal}
diff --git a/man/style_dir.Rd b/man/style_dir.Rd
index 443252be7..78e3a60d9 100644
--- a/man/style_dir.Rd
+++ b/man/style_dir.Rd
@@ -1,5 +1,5 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/ui.R
+% Please edit documentation in R/ui-styling.R
 \name{style_dir}
 \alias{style_dir}
 \title{Prettify arbitrary R code}
diff --git a/man/style_file.Rd b/man/style_file.Rd
index add8b73f2..3fb2d06d3 100644
--- a/man/style_file.Rd
+++ b/man/style_file.Rd
@@ -1,5 +1,5 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/ui.R
+% Please edit documentation in R/ui-styling.R
 \name{style_file}
 \alias{style_file}
 \title{Style \code{.R}, \code{.Rmd} or \code{.Rnw} files}
diff --git a/man/style_pkg.Rd b/man/style_pkg.Rd
index b77d94ed9..dc6fe9603 100644
--- a/man/style_pkg.Rd
+++ b/man/style_pkg.Rd
@@ -1,5 +1,5 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/ui.R
+% Please edit documentation in R/ui-styling.R
 \name{style_pkg}
 \alias{style_pkg}
 \title{Prettify R source code}
diff --git a/man/style_text.Rd b/man/style_text.Rd
index 4c4fbc8a2..4f4eeff55 100644
--- a/man/style_text.Rd
+++ b/man/style_text.Rd
@@ -1,5 +1,5 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/ui.R
+% Please edit documentation in R/ui-styling.R
 \name{style_text}
 \alias{style_text}
 \title{Style a string}
diff --git a/tests/testthat/helpers-devel-options.R b/tests/testthat/helpers-devel-options.R
new file mode 100644
index 000000000..8751489f7
--- /dev/null
+++ b/tests/testthat/helpers-devel-options.R
@@ -0,0 +1,2 @@
+cat("In tests/testthat/helpers-devel-options: ")
+cache_deactivate()
diff --git a/tests/testthat/reference-objects/cache-info-1 b/tests/testthat/reference-objects/cache-info-1
new file mode 100644
index 000000000..724c65e0a
Binary files /dev/null and b/tests/testthat/reference-objects/cache-info-1 differ
diff --git a/tests/testthat/reference-objects/cache-info-2 b/tests/testthat/reference-objects/cache-info-2
new file mode 100644
index 000000000..5bf3a665d
Binary files /dev/null and b/tests/testthat/reference-objects/cache-info-2 differ
diff --git a/tests/testthat/reference-objects/cache-info-3 b/tests/testthat/reference-objects/cache-info-3
new file mode 100644
index 000000000..edda7ba76
Binary files /dev/null and b/tests/testthat/reference-objects/cache-info-3 differ
diff --git a/tests/testthat/reference-objects/caching.R b/tests/testthat/reference-objects/caching.R
new file mode 100644
index 000000000..a121ebd67
--- /dev/null
+++ b/tests/testthat/reference-objects/caching.R
@@ -0,0 +1,33 @@
+#' CHan deng
+#'
+#' Performs various izil
+#' @examples
+#' zz + 1
+#' \dontrun{
+#' xfun::xxio(fun(77), file)
+#' }
+#' dplyr::filter(x == 3, zz = max(.data$`5`, na.rom = TRUE))
+#' \dontrun{
+#' unlink(file2)
+#' }
+#' \dontrun{
+#' {
+#'   x
+#' }
+#' unlink(file2)
+#' }
+xxtt <- function(bli, bla, blup = 3) {
+  changed <- withr::tzu(
+    zname(path),
+    condense_files(x_basename(path), c_transformers)
+  )
+  visible(chan)
+}
+
+g <- 33
+
+z <- fun(g, z = xxtt)
+
+if (not(x) == 9) {
+  cache_this_file()
+}
diff --git a/tests/testthat/test-cache-with-r-cache.R b/tests/testthat/test-cache-with-r-cache.R
new file mode 100644
index 000000000..f0a9ab347
--- /dev/null
+++ b/tests/testthat/test-cache-with-r-cache.R
@@ -0,0 +1,164 @@
+styler_version <- utils::packageDescription("styler", fields = "Version")
+clear_testthat_cache <- purrr::partial(cache_clear, "testthat", ask = FALSE)
+
+capture.output(test_that("No warnings are issued when R.cache is installed", {
+  skip_if_not_installed("R.cache")
+  on.exit(clear_testthat_cache())
+  expect_silent(assert_R.cache_installation(installation_only = TRUE))
+  expect_silent(assert_R.cache_installation())
+  expect_warning(style_text("1+1"), NA)
+  expect_warning(cache_activate("testthat"), NA)
+  expect_warning(style_text("1+1"), NA)
+  expect_silent(assert_R.cache_installation(installation_only = TRUE))
+  expect_silent(assert_R.cache_installation())
+}))
+
+capture.output(test_that("Cache management works when R.cache is installed", {
+  skip_if_not_installed("R.cache")
+  on.exit(clear_testthat_cache())
+  clear_testthat_cache()
+  # clearing a cache inactivates the caching functionality.
+  expect_false(cache_info(format = "tabular")$activated)
+  cache_activate("testthat")
+  # at fresh startup, with R.cache installed
+  expect_s3_class(cache_info(format = "tabular"), "tbl_df")
+  expect_error(cache_info(), NA)
+  expect_equal(basename(cache_activate()), styler_version)
+  expect_equal(basename(cache_activate("xyz")), "xyz")
+  expect_equal(getOption("styler.cache_name"), "xyz")
+  # when cache xyz is activated, cache_info() shows deactivated for other caches
+  expect_false(cache_info(styler_version, format = "tabular")$activated)
+  expect_error(cache_info(format = "lucid"), NA)
+  # cache_info() defaults to the currently active cache
+  expect_equal(basename(cache_info(format = "tabular")$location), "xyz")
+
+  cache_deactivate()
+  # cache_info() defaults to the cache of the version of styler if
+  # not cache is active
+  expect_equal(
+    basename(cache_info(format = "tabular")$location), styler_version
+  )
+  expect_false(cache_info(format = "tabular")$activated)
+  expect_equal(getOption("styler.cache_location"), NULL)
+  expect_error(cache_clear(ask = FALSE), NA)
+}))
+
+
+
+capture.output(test_that("activated cache brings speedup on style_file() API", {
+  skip_if_not_installed("R.cache")
+  cache_activate("testthat")
+  on.exit(clear_testthat_cache())
+  clear_testthat_cache()
+  cache_activate("testthat")
+  first <- system.time(styler::style_file(test_path("reference-objects/caching.R")))
+  second <- system.time(styler::style_file(test_path("reference-objects/caching.R")))
+  expect_true(first["elapsed"] / 2 > second["elapsed"])
+}))
+
+text <- c(
+  "#' Roxygen",
+  "#' Comment",
+  "#' @examples",
+  "#' 1 + 1",
+  "k <- function() {",
+  "  1 + 1",
+  "  if (x) {",
+  "    k()",
+  "  }",
+  "}",
+  ""
+) %>%
+  rep(10)
+
+capture.output(test_that("activated cache brings speedup on style_text() API on character vector", {
+  skip_if_not_installed("R.cache")
+  cache_activate("testthat")
+  on.exit(clear_testthat_cache())
+  clear_testthat_cache()
+  cache_activate("testthat")
+
+  first <- system.time(styler::style_text(text))
+  second <- system.time(styler::style_text(text))
+  expect_true(first["elapsed"] / 2 > second["elapsed"])
+}))
+
+capture.output(test_that("activated cache brings speedup on style_text() API on character scalar", {
+  skip_if_not_installed("R.cache")
+  cache_activate("testthat")
+  on.exit(clear_testthat_cache())
+  clear_testthat_cache()
+  cache_activate("testthat")
+
+  first <- system.time(styler::style_text(paste0(text, collapse = "\n")))
+  second <- system.time(styler::style_text(paste0(text, collapse = "\n")))
+  expect_true(first["elapsed"] / 2 > second["elapsed"])
+}))
+
+
+capture.output(test_that("no speedup when tranformer changes", {
+  skip_if_not_installed("R.cache")
+  cache_activate("testthat")
+  on.exit(clear_testthat_cache())
+  clear_testthat_cache()
+  cache_activate("testthat")
+  t1 <- tidyverse_style()
+  first <- system.time(style_text(text, transformers = t1))
+  t1$use_raw_indention <- !t1$use_raw_indention
+  second <- system.time(style_text(text, transformers = t1))
+  expect_false(first["elapsed"] / 2 > second["elapsed"])
+}))
+
+
+capture.output(
+  test_that(paste0(
+    "activated cache brings speedup on style_text() API on ",
+    "character scalar and character vector (mixed)"
+  ), {
+  skip_if_not_installed("R.cache")
+  cache_activate("testthat")
+  on.exit(clear_testthat_cache())
+  clear_testthat_cache()
+  cache_activate("testthat")
+
+  first <- system.time(styler::style_text(text))
+  second <- system.time(styler::style_text(paste0(text, collapse = "\n")))
+  expect_true(first["elapsed"] / 2 > second["elapsed"])
+}))
+
+
+capture.output(test_that("unactivated cache does not bring speedup", {
+  skip_if_not_installed("R.cache")
+  on.exit(clear_testthat_cache)
+  clear_testthat_cache()
+  cache_deactivate()
+  first <- system.time(styler::style_file(test_path("reference-objects/caching.R")))
+  second <- system.time(styler::style_file(test_path("reference-objects/caching.R")))
+  expect_false(first["elapsed"] / 2 > second["elapsed"])
+}))
+
+capture.output(test_that("cached expressions are displayed propperly", {
+  on.exit(clear_testthat_cache())
+  clear_testthat_cache()
+  cache_info <- cache_info("testthat", format = "tabular")
+  expect_known_value(
+    cache_info[, c("n", "size", "last_modified", "activated")],
+    file = test_path("reference-objects/cache-info-1")
+  )
+
+  cache_activate("testthat")
+  style_text("1+1")
+  cache_info <- cache_info(format = "tabular")
+  cache_info$size <- round(cache_info$size, -2)
+  expect_known_value(
+    cache_info[, c("n", "size", "activated")],
+    file = test_path("reference-objects/cache-info-2")
+  )
+  style_text("a <-function() NULL")
+  cache_info <- cache_info(format = "tabular")
+  cache_info$size <- round(cache_info$size, -2)
+  expect_known_value(
+    cache_info[, c("n", "size", "activated")],
+    file = test_path("reference-objects/cache-info-3")
+  )
+}))
diff --git a/tests/testthat/test-cache-without-r-cache.R b/tests/testthat/test-cache-without-r-cache.R
new file mode 100644
index 000000000..955ae84bb
--- /dev/null
+++ b/tests/testthat/test-cache-without-r-cache.R
@@ -0,0 +1,41 @@
+test_that("Cache management fails mostly when R.cache is not installed", {
+  skip_if(rlang::is_installed("R.cache"))
+  expect_error(cache_info(), "is needed when the caching feature is activated")
+  expect_error(cache_activate(), "is needed when the caching feature is activated")
+  expect_error(cache_clear(), "is needed when the caching feature is activated")
+  expect_error(capture.output(cache_deactivate()), NA)
+  expect_silent(assert_R.cache_installation())
+  expect_error(
+    assert_R.cache_installation(installation_only = TRUE),
+    "is needed when the caching feature is activated"
+  )
+})
+
+
+test_that("styling works when R.cache is not installed", {
+  skip_if(rlang::is_installed("R.cache"))
+  # warning for first time
+  expect_warning(
+    capture.output(
+      withr::with_options(
+        # simulate .onLoad() in fresh R session
+        list(styler.cache_name = cache_derive_name()),
+        style_text("1+1")
+      )
+    ),
+    "Deactivating the caching feature for the current session"
+  )
+
+  # No warnings subsequently
+  expect_warning(
+    capture.output(
+      withr::with_options(
+        list(styler.cache_name = cache_derive_name()), {
+          suppressWarnings(style_text("1+1"))
+          style_text("1+1")
+        }
+      )
+    ),
+    NA
+  )
+})