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, 32 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_vector_set.hh b/source/blender/blenlib/BLI_vector_set.hh
index 2f5d04aefa2..567e4fd8128 100644
--- a/source/blender/blenlib/BLI_vector_set.hh
+++ b/source/blender/blenlib/BLI_vector_set.hh
@@ -415,6 +415,38 @@ class VectorSet {
   }
 
   /**
+   * Returns the key that is stored in the vector set that compares equal to the given key. This
+   * invokes undefined behavior when the key is not in the set.
+   */
+  const Key &lookup_key(const Key &key) const
+  {
+    return this->lookup_key_as(key);
+  }
+  template<typename ForwardKey> const Key &lookup_key_as(const ForwardKey &key) const
+  {
+    const Key *key_ptr = this->lookup_key_ptr_as(key);
+    BLI_assert(key_ptr != nullptr);
+    return *key_ptr;
+  }
+
+  /**
+   * Returns a pointer to the key that is stored in the vector set that compares equal to the given
+   * key. If the key is not in the set, null is returned.
+   */
+  const Key *lookup_key_ptr(const Key &key) const
+  {
+    return this->lookup_key_ptr_as(key);
+  }
+  template<typename ForwardKey> const Key *lookup_key_ptr_as(const ForwardKey &key) const
+  {
+    const int64_t index = this->index_of_try__impl(key, hash_(key));
+    if (index >= 0) {
+      return keys_ + index;
+    }
+    return nullptr;
+  }
+
+  /**
    * Get a pointer to the beginning of the array containing all keys.
    */
   const Key *data() const