From cb94cb70ec113b164ea156c2961b7cdcf7391fcf Mon Sep 17 00:00:00 2001
From: Peter Arato <it.arato@gmail.com>
Date: Tue, 20 Jan 2015 22:32:02 +0000
Subject: [PATCH] Add lazy loader and cached func factory.

---
 cachematrix.R | 53 +++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 45 insertions(+), 8 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..ec894900def 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,52 @@
-## Put comments here that give an overall description of what your
-## functions do
+## This solution ignores the one required by the assignment. I believe this
+## solution is more flexible. That one is working with fixed function and
+## arguments.
+## This code presents two alternatives.
 
-## Write a short comment describing this function
 
-makeCacheMatrix <- function(x = matrix()) {
+## Creates a version of a function that is able to cache the result per key.
+## This allows making a cachable version of any function.
+## Useful when the calling arguments are expected to change.
+## Input
+##  - f function
+## Return
+##  - callable function, arguments: cache key, original function arguments
+cachedFunctionFactory <- function(f) {
+  cache = list()
+  function(key, ...) {
+    if (is.null(cache[[key]])) {
+      cache[[key]] <<- f(...)
+    }
+    cache[[key]]
+  }
+}
 
+## Lazy loader generator.
+## Accepts any function with the called arguments.
+## Useful when the arguments will not change.
+## Input
+##  - f function
+##  - ... function args
+## Return
+##  - callable lazy evaluator
+lazyLoadingFactory <- function(f, ...) {
+  cache = NULL
+  function() {
+    if (is.null(cache)) {
+      cache <<- f(...)
+    }
+    cache
+  }
 }
 
 
-## Write a short comment describing this function
+## Example to matrix to invert.
+m <- matrix(c(2, 5, 1, 2), 2, 2)
 
-cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+## Example of using the cached function loader:
+cachableSolve <- cachedFunctionFactory(solve)
+cachedSolve("key", m)
+
+## Example of using the lazy loader:
+lazySolve <- lazyLoadingFactory(solve, m)
+lazySolve()
\ No newline at end of file