diff --git a/develop/untests/registry_untests.lua b/develop/untests/registry_untests.lua
index 438c982..5a2f69c 100644
--- a/develop/untests/registry_untests.lua
+++ b/develop/untests/registry_untests.lua
@@ -365,6 +365,56 @@ do
     assert(e.__chunk == nil)
 end
 
+do
+    local f1, f2 = evo.registry.entity(), evo.registry.entity()
+    local e = evo.registry.entity()
+
+    local function mul2(v) return v * 2 end
+    local function null(_) end
+
+    do
+        assert(not e:apply(f1, mul2))
+        assert(e.__chunk == nil)
+        assert(not e:apply(f1, null))
+        assert(e.__chunk == nil)
+
+        assert(e:insert(f1, 21))
+        assert(e:get(f1) == 21)
+        assert(e.__chunk == evo.registry.chunk(f1))
+
+        assert(e:apply(f1, mul2))
+        assert(e:get(f1) == 42)
+        assert(e.__chunk == evo.registry.chunk(f1))
+
+        assert(e:apply(f1, null))
+        assert(e:get(f1) == true)
+        assert(e.__chunk == evo.registry.chunk(f1))
+    end
+
+    do
+        assert(not e:apply(f2, mul2))
+        assert(e:get(f1) == true)
+        assert(e.__chunk == evo.registry.chunk(f1))
+        assert(not e:apply(f2, null))
+        assert(e:get(f1) == true)
+        assert(e.__chunk == evo.registry.chunk(f1))
+
+        assert(e:insert(f2, 4))
+        assert(e:get(f2) == 4)
+        assert(e.__chunk == evo.registry.chunk(f1, f2))
+
+        assert(e:apply(f2, mul2))
+        assert(e:get(f1) == true)
+        assert(e:get(f2) == 8)
+        assert(e.__chunk == evo.registry.chunk(f1, f2))
+
+        assert(e:apply(f2, null))
+        assert(e:get(f1) == true)
+        assert(e:get(f2) == true)
+        assert(e.__chunk == evo.registry.chunk(f1, f2))
+    end
+end
+
 for _ = 1, 100 do
     local insert_fragments = {} ---@type evolved.entity[]
     local insert_fragment_count = math.random(0, 10)
diff --git a/evolved/registry.lua b/evolved/registry.lua
index 0aff1bd..4bfe353 100644
--- a/evolved/registry.lua
+++ b/evolved/registry.lua
@@ -465,9 +465,9 @@ end
 ---@return boolean
 ---@nodiscard
 function registry.has(entity, fragment)
-    local cur_chunk = entity.__chunk
-    if cur_chunk == nil then return false end
-    return __chunk_has_fragment(cur_chunk, fragment)
+    local chunk = entity.__chunk
+    if chunk == nil then return false end
+    return __chunk_has_fragment(chunk, fragment)
 end
 
 ---@param entity evolved.entity
@@ -475,9 +475,9 @@ end
 ---@return boolean
 ---@nodiscard
 function registry.has_all(entity, ...)
-    local cur_chunk = entity.__chunk
-    if cur_chunk == nil then return select('#', ...) == 0 end
-    return __chunk_has_all_fragments(cur_chunk, ...)
+    local chunk = entity.__chunk
+    if chunk == nil then return select('#', ...) == 0 end
+    return __chunk_has_all_fragments(chunk, ...)
 end
 
 ---@param entity evolved.entity
@@ -485,9 +485,9 @@ end
 ---@return boolean
 ---@nodiscard
 function registry.has_any(entity, ...)
-    local cur_chunk = entity.__chunk
-    if cur_chunk == nil then return false end
-    return __chunk_has_any_fragments(cur_chunk, ...)
+    local chunk = entity.__chunk
+    if chunk == nil then return false end
+    return __chunk_has_any_fragments(chunk, ...)
 end
 
 ---@param entity evolved.entity
@@ -495,7 +495,23 @@ end
 ---@param transform fun(any): any
 ---@return boolean is_applied
 function registry.apply(entity, fragment, transform)
-    error('not impl yet', 2)
+    if not idpools.alive(__guids, entity.__guid) then
+        return false
+    end
+
+    local chunk = entity.__chunk
+    if chunk == nil then return false end
+
+    local components = chunk.__components[fragment]
+    if components == nil then return false end
+
+    local component = components[entity.__index_in_chunk]
+
+    component = transform(component)
+    component = component == nil and true or component
+
+    components[entity.__index_in_chunk] = component
+    return true
 end
 
 ---@param query evolved.query