From b08ef4d61e0dde98995ec3d2f69a4447255e79ef Mon Sep 17 00:00:00 2001
From: Yaroslav Rogov <rogovyaroslav@gmail.com>
Date: Tue, 14 Sep 2021 11:09:50 +0300
Subject: [PATCH] Add genlib_map:search/2 (#36)

* feat: Add genlib_map:search/2

* deps: Update tools deps and fix formatting

* fix: Change return type
---
 rebar.config               |  6 ++---
 src/genlib_format.erl      |  8 +++---
 src/genlib_map.erl         | 15 ++++++++++++
 test/genlib_pmap_tests.erl |  2 +-
 test/prop_genlib_map.erl   | 50 +++++++++++++++++++++++++++++++++++---
 5 files changed, 70 insertions(+), 11 deletions(-)

diff --git a/rebar.config b/rebar.config
index b8fde48..bb775cc 100644
--- a/rebar.config
+++ b/rebar.config
@@ -39,9 +39,9 @@
 ]}.
 
 {plugins, [
-    {erlfmt, "0.8.0"},
-    {rebar3_proper, "0.12.0"},
-    {rebar3_lint, "0.4.0"}
+    {erlfmt, "1.0.0"},
+    {rebar3_proper, "0.12.1"},
+    {rebar3_lint, "0.5.0"}
 ]}.
 
 {erlfmt, [
diff --git a/src/genlib_format.erl b/src/genlib_format.erl
index 19568c2..baaf651 100644
--- a/src/genlib_format.erl
+++ b/src/genlib_format.erl
@@ -240,11 +240,13 @@ binary_to_hex(V, false) ->
 
 binary_to_hex_(V, A) ->
     <<
-        <<(if
+        <<
+            (if
                 C >= 10 -> C + A - 10;
                 true -> C + $0
-            end)>>
-        || <<C:4>> <= V
+            end)
+        >>
+     || <<C:4>> <= V
     >>.
 
 -spec hex_to_binary(binary()) -> binary().
diff --git a/src/genlib_map.erl b/src/genlib_map.erl
index 1626945..48274bc 100644
--- a/src/genlib_map.erl
+++ b/src/genlib_map.erl
@@ -18,6 +18,7 @@
 -export([binarize/2]).
 -export([diff/2]).
 -export([fold_while/3]).
+-export([search/2]).
 
 %%
 
@@ -161,3 +162,17 @@ do_fold_while(Fun, Acc, Iter) ->
                 {cont, NextAcc} -> do_fold_while(Fun, NextAcc, NextIter)
             end
     end.
+
+%% @doc Like lists:search, but for maps to reduce memory pressure
+%% (comparing to naive implementation with conversion to list)
+-spec search(fun((K, V) -> boolean()), #{K => V}) -> false | {K, V}.
+search(Fun, Map) when is_function(Fun, 2), is_map(Map) ->
+    do_search(Fun, maps:next(maps:iterator(Map))).
+
+do_search(_Fun, none) ->
+    false;
+do_search(Fun, {Key, Value, Iter}) ->
+    case Fun(Key, Value) of
+        true -> {Key, Value};
+        false -> do_search(Fun, maps:next(Iter))
+    end.
diff --git a/test/genlib_pmap_tests.erl b/test/genlib_pmap_tests.erl
index 392d1ca..fc51aa7 100644
--- a/test/genlib_pmap_tests.erl
+++ b/test/genlib_pmap_tests.erl
@@ -127,7 +127,7 @@ no_leftovers_test() ->
         receive
             {worker, Pid} -> Pid
         end
-        || _ <- Ns
+     || _ <- Ns
     ],
     _ = exit(RunnerPid, enough),
     % lazy, i know
diff --git a/test/prop_genlib_map.erl b/test/prop_genlib_map.erl
index 6929444..e20b62e 100644
--- a/test/prop_genlib_map.erl
+++ b/test/prop_genlib_map.erl
@@ -6,11 +6,9 @@
 prop_fold_while() ->
     ?FORALL(
         Map,
-        ?LET(KVList, non_empty(list({term(), term()})), maps:from_list(KVList)),
+        non_empty_map(),
         begin
-            RandomId = rand:uniform(map_size(Map)),
-            {RandomKey, RandomValue} = lists:nth(RandomId, maps:to_list(Map)),
-
+            {RandomKey, RandomValue} = random_map_pair(Map),
             Result =
                 genlib_map:fold_while(
                     fun
@@ -24,3 +22,47 @@ prop_fold_while() ->
             Result =:= RandomValue
         end
     ).
+
+-spec prop_search_found() -> proper:test().
+prop_search_found() ->
+    ?FORALL(
+        Map,
+        non_empty_map(),
+        begin
+            {RandomKey, RandomValue} = random_map_pair(Map),
+            Result =
+                genlib_map:search(
+                    fun(K, _V) -> K =:= RandomKey end,
+                    Map
+                ),
+
+            {RandomKey, RandomValue} =:= Result
+        end
+    ).
+
+-spec prop_search_not_found() -> proper:test().
+prop_search_not_found() ->
+    ?FORALL(
+        Map,
+        map(),
+        begin
+            NonExistentKey = make_ref(),
+            Result =
+                genlib_map:search(
+                    fun(K, _V) -> K =:= NonExistentKey end,
+                    Map
+                ),
+
+            false =:= Result
+        end
+    ).
+
+map() ->
+    ?LET(KVList, list({term(), term()}), maps:from_list(KVList)).
+
+non_empty_map() ->
+    ?LET(KVList, non_empty(list({term(), term()})), maps:from_list(KVList)).
+
+random_map_pair(Map) ->
+    RandomId = rand:uniform(map_size(Map)),
+    lists:nth(RandomId, maps:to_list(Map)).