From c0364c3e8025e60c1bb50c5075ad11ce97c3e165 Mon Sep 17 00:00:00 2001
From: rmorshea <ryan.morshead@gmail.com>
Date: Tue, 22 Nov 2022 16:03:00 -0800
Subject: [PATCH] remove IDOM_FEATURE_INDEX_AS_DEFAULT_KEY opt

---
 docs/source/about/changelog.rst |  4 +++-
 src/idom/config.py              | 16 ----------------
 src/idom/core/layout.py         | 19 ++-----------------
 3 files changed, 5 insertions(+), 34 deletions(-)

diff --git a/docs/source/about/changelog.rst b/docs/source/about/changelog.rst
index 415a16699..9af5293b2 100644
--- a/docs/source/about/changelog.rst
+++ b/docs/source/about/changelog.rst
@@ -23,7 +23,9 @@ more info, see the :ref:`Contributor Guide <Creating a Changelog Entry>`.
 Unreleased
 ----------
 
-No changes.
+**Removed**
+
+- :pull:`840` - remove ``IDOM_FEATURE_INDEX_AS_DEFAULT_KEY`` option
 
 
 v0.41.0
diff --git a/src/idom/config.py b/src/idom/config.py
index dec2cb958..950b7402c 100644
--- a/src/idom/config.py
+++ b/src/idom/config.py
@@ -62,22 +62,6 @@
 )
 """This has been renamed to :data:`IDOM_WEB_MODULES_DIR`"""
 
-IDOM_FEATURE_INDEX_AS_DEFAULT_KEY = _Option(
-    "IDOM_FEATURE_INDEX_AS_DEFAULT_KEY",
-    default=True,
-    mutable=False,
-    validator=lambda x: bool(int(x)),
-)
-"""Use the index of elements/components amongst their siblings as the default key.
-
-The flag's default value is set to true. To return to legacy behavior set
-``IDOM_FEATURE_INDEX_AS_DEFAULT_KEY=0``. In a future release, this flag will be removed
-entirely and the indices will always be the default key.
-
-For more information on changes to this feature flag see:
-https://github.com/idom-team/idom/issues/351
-"""
-
 IDOM_TESTING_DEFAULT_TIMEOUT = _Option(
     "IDOM_TESTING_DEFAULT_TIMEOUT",
     5.0,
diff --git a/src/idom/core/layout.py b/src/idom/core/layout.py
index 38bdd6490..4a2561190 100644
--- a/src/idom/core/layout.py
+++ b/src/idom/core/layout.py
@@ -24,11 +24,7 @@
 from uuid import uuid4
 from weakref import ref as weakref
 
-from idom.config import (
-    IDOM_CHECK_VDOM_SPEC,
-    IDOM_DEBUG_MODE,
-    IDOM_FEATURE_INDEX_AS_DEFAULT_KEY,
-)
+from idom.config import IDOM_CHECK_VDOM_SPEC, IDOM_DEBUG_MODE
 from idom.utils import Ref
 
 from ._event_proxy import _wrap_in_warning_event_proxies
@@ -755,7 +751,7 @@ def _process_child_type_and_key(
             key = None
 
         if key is None:
-            key = _default_key(index)
+            key = index
 
         yield (child, child_type, key)
 
@@ -765,14 +761,3 @@ def _process_child_type_and_key(
 _DICT_TYPE = _ElementType(1)
 _COMPONENT_TYPE = _ElementType(2)
 _STRING_TYPE = _ElementType(3)
-
-
-if IDOM_FEATURE_INDEX_AS_DEFAULT_KEY.current:
-
-    def _default_key(index: int) -> Any:
-        return index
-
-else:
-
-    def _default_key(index: int) -> Any:  # pragma: no cover
-        return object()