implement cache_redis()

DESCRIPTION

@@ -19,6 +19,7 @@ Suggests:
     aws.s3,
     httr,
     covr,
-    googleCloudStorageR
+    googleCloudStorageR,
+    redux
 License: MIT + file LICENSE
 RoxygenNote: 6.0.1

NAMESPACE

@@ -4,6 +4,7 @@ S3method(print,memoised)
 export(cache_filesystem)
 export(cache_gcs)
 export(cache_memory)
+export(cache_redis)
 export(cache_s3)
 export(forget)
 export(has_cache)

R/cache_redis.R

@@ -0,0 +1,55 @@
+#' Redis Cache
+#'
+#' Use a Redis based cache to persist memoisation between R sessions.
+#'
+#' @param ... arguments passed along to the `hiredis()` function in the **redux** package.
+#' @inheritParams cache_memory
+#' @author Carson Sievert
+#' @export
+#' @examples
+#'
+#' \dontrun{
+#' my_function <- memoise::memoise(
+#'   function(input) {
+#'     Sys.sleep(5)
+#'     paste('Input was', input)
+#'   },
+#'   cache = cache_redis()
+#' )
+#' my_function("a")
+#' my_function("a")
+#'
+#' }
+cache_redis <- function(..., algo = "md5") {
+
+  if (!requireNamespace("redux")) {
+    stop("Package `redux` must be installed for `cache_redis()`. Please install and try again.")
+  } # nocov
+
+  r <- redux::hiredis(...)
+
+  cache_reset <- function() {
+    r$FLUSHALL()
+  }
+
+  cache_set <- function(key, value) {
+    r$SET(key, redux::object_to_bin(value))
+  }
+
+  cache_get <- function(key) {
+    redux::bin_to_object(r$GET(key))
+  }
+
+  cache_has_key <- function(key) {
+    length(r$KEYS(key)) == 1
+  }
+
+  list(
+    digest = function(...) digest::digest(..., algo = algo),
+    reset = cache_reset,
+    set = cache_set,
+    get = cache_get,
+    has_key = cache_has_key,
+    keys = function() r$KEYS("*")
+  )
+}