Hash the function body as well as the arguments

This ensures functions with identical arguments will not have the same
cache.

Fixes #38

NEWS.md

@@ -1,5 +1,7 @@
 # Version 1.0.0
 
+* Caches now hash the function body along with the arguments, to ensure
+  functions with identical arguments use a separate file-system cache. (#38)
 * Handle missing arguments in memoised functions for simple cases not using
   non-standard-evaluation (#19).
 * `memoise()` gains a `cache=` argument to specify an external cache. Two types

R/memoise.R

@@ -131,7 +131,7 @@ memoise <- memoize <- function(f, ..., envir = environment(f), cache = cache_mem
       args <- c(lapply(called_args, eval, parent.frame()),
         lapply(default_args, eval, envir = environment()))
 
-      hash <- `_cache`$digest(c(args,
+      hash <- `_cache`$digest(c(body(`_f`), args,
           lapply(`_additional`, function(x) eval(x[[2L]], environment(x)))))
 
       if (`_cache`$has_key(hash)) {

tests/testthat/test-filesystem.R

@@ -22,3 +22,17 @@ test_that("using a filesystem cache works", {
   expect_true(is.memoised(fnm))
   expect_false(is.memoised(fn))
 })
+
+test_that("two functions with the same arguments produce different caches (#38)", {
+
+  temp <- tempfile()
+  fs <- cache_filesystem(temp)
+
+  f1 <- memoise(function() 1, cache = fs)
+  f2 <- memoise(function() 2, cache = fs)
+
+  expect_equal(f1(), 1)
+  expect_equal(f2(), 2)
+
+  expect_equal(length(list.files(temp)), 2)
+})