From 70cf8e86a06d8721fcc8b658bb2be1f7b401326f Mon Sep 17 00:00:00 2001
From: Siraaj Khandkar <siraaj@khandkar.net>
Date: Thu, 14 Aug 2014 13:55:40 -0400
Subject: [PATCH] Add dictionary method: pop.

---
 src/hope_dictionary.erl     | 3 +++
 src/hope_kv_list.erl        | 7 +++++++
 test/hope_kv_list_SUITE.erl | 8 ++++++++
 3 files changed, 18 insertions(+)

diff --git a/src/hope_dictionary.erl b/src/hope_dictionary.erl
index 5494f39..7930c1d 100644
--- a/src/hope_dictionary.erl
+++ b/src/hope_dictionary.erl
@@ -21,6 +21,9 @@
 -callback update(t(K, V), K, fun((hope_option:t(V)) -> V)) ->
     t(K, V).
 
+-callback pop(t(K, V), K) ->
+    {hope_option:t(V), t(K, V)}.
+
 -callback map(t(K, V), fun((K, V) -> V)) ->
     t(K, V).
 
diff --git a/src/hope_kv_list.erl b/src/hope_kv_list.erl
index 3ca9d07..ebc4176 100644
--- a/src/hope_kv_list.erl
+++ b/src/hope_kv_list.erl
@@ -14,6 +14,7 @@
     , get/2
     , set/3
     , update/3
+    , pop/2
     , iter/2
     , map/2
     , filter/2
@@ -51,6 +52,12 @@ update(T, K, F) ->
     % TODO: Eliminate the 2nd lookup.
     set(T, K, V2).
 
+pop(T1, K) ->
+    case lists:keytake(K, 1, T1)
+    of  {value, {K, V}, T2} -> {{some, V}, T2}
+    ;   false               -> {none     , T1}
+    end.
+
 iter(T, F1) ->
     F2 = lift_map(F1),
     lists:foreach(F2, T).
diff --git a/test/hope_kv_list_SUITE.erl b/test/hope_kv_list_SUITE.erl
index e0f0747..8abb888 100644
--- a/test/hope_kv_list_SUITE.erl
+++ b/test/hope_kv_list_SUITE.erl
@@ -10,6 +10,7 @@
 -export(
     [ t_set_new/1
     , t_set_existing/1
+    , t_pop/1
     ]).
 
 
@@ -30,6 +31,7 @@ groups() ->
     Tests =
         [ t_set_new
         , t_set_existing
+        , t_pop
         ],
     Properties = [],
     [{?GROUP_KV_LIST, Properties, Tests}].
@@ -55,3 +57,9 @@ t_set_existing(_Config) ->
     ListResulting = hope_kv_list:set(ListInitial, Key, ValExpected),
     {some, ValResulting} = hope_kv_list:get(ListResulting, Key),
     ValResulting = ValExpected.
+
+t_pop(_Config) ->
+    KVList = [{a, 1}, {b, 2}, {c, 3}],
+    Dict1 = hope_kv_list:of_kv_list(KVList),
+    {{some, 1},  Dict2} = hope_kv_list:pop(Dict1, a),
+    {none     , _Dict3} = hope_kv_list:pop(Dict2, a).
-- 
2.20.1