BLI: support looking up a key stored in Map or VectorSet

Sometimes it is useful to find the key that compares equal
to a known key. Typically that happens when the key itself
has additional data attached that is not part of its hash.

Note that the returned key reference/pointer is const, because
the caller must not change the key in a way that changes its
hash or how it compares to other keys.

1 files changed, 13 insertions, 0 deletions

diff --git a/source/blender/blenlib/tests/BLI_map_test.cc b/source/blender/blenlib/tests/BLI_map_test.cc
index 18be456bd20..679a10e9ce0 100644
--- a/source/blender/blenlib/tests/BLI_map_test.cc
+++ b/source/blender/blenlib/tests/BLI_map_test.cc
@@ -640,6 +640,19 @@ TEST(map, RemoveDuringIteration)
   EXPECT_EQ(map.lookup(3), 3);
 }
 
+TEST(map, LookupKey)
+{
+  Map<std::string, int> map;
+  map.add("a", 0);
+  map.add("b", 1);
+  map.add("c", 2);
+  EXPECT_EQ(map.lookup_key("a"), "a");
+  EXPECT_EQ(map.lookup_key_as("c"), "c");
+  EXPECT_EQ(map.lookup_key_ptr_as("d"), nullptr);
+  EXPECT_EQ(map.lookup_key_ptr_as("b")->size(), 1);
+  EXPECT_EQ(map.lookup_key_ptr("a"), map.lookup_key_ptr_as("a"));
+}
+
 /**
  * Set this to 1 to activate the benchmark. It is disabled by default, because it prints a lot.
  */