Add When Overflow Is Desired as a clojure til.

README.md

@@ -18,6 +18,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Splitting On Whitespace](clojure/splitting-on-whitespace.md)
 - [Swap Two Items in a Vector](clojure/swap-two-items-in-a-vector.md)
 - [Type of Anything](clojure/type-of-anything.md)
+- [When Overflow Is Desired](clojure/when-overflow-is-desired.md)
 
 ### devops
 

clojure/when-overflow-is-desired.md

@@ -0,0 +1,18 @@
+# When Overflow Is Desired
+
+If you try to add two `MAX_VALUE` Longs, Clojure is kind enough to warn you.
+
+```clojure
+> (+ Long/MAX_VALUE Long/MAX_VALUE)
+ArithmeticException integer overflow  clojure.lang.Numbers.throwIntOverflow (Numbers.java:1424)
+```
+
+However, when overflow is desired, you can use the *unchecked* operators
+(e.g. `unchecked-add`).
+
+```clojure
+> (unchecked-add Long/MAX_VALUE Long/MAX_VALUE)
+-2
+```
+
+See also `unchecked-subtract` and `unchecked-multiply`.