Using sets instead of arrays and empty? instead of any?

lib/zeitwerk/loader.rb

@@ -539,17 +539,17 @@ def all_dirs
       # If manual incepted namespaces are present we skip the default behavior
       # and we will only incept the manually defined namespaces for improved
       # performance
-      if manual_incepted_namespaces.any?
-        if manual_incepted_namespaces.include?(cref.cname.name)
-          Registry.register_inception(cref.path, abspath, self)
-        end
-      else
+      if manual_incepted_namespaces.empty?
         # This operation can impact performance in big codebases since it will
         # be evaluated for every single auoloaded constant.
         # See why in the documentation of Zeitwerk::Registry.inceptions.
         unless cref.autoload?
           Registry.register_inception(cref.path, abspath, self)
         end
+      else
+        if manual_incepted_namespaces.include?(cref.cname.name)
+          Registry.register_inception(cref.path, abspath, self)
+        end
       end
     end
 

lib/zeitwerk/loader/config.rb

@@ -13,7 +13,7 @@ module Zeitwerk::Loader::Config
   # @sig #call | #debug | nil
   attr_accessor :logger
 
-  # @sig nil
+  # @sig Set[String]
   attr_accessor :manual_incepted_namespaces
 
   # Absolute paths of the root directories, mapped to their respective root namespaces:
@@ -89,7 +89,7 @@ module Zeitwerk::Loader::Config
   def initialize
     @inflector                  = Zeitwerk::Inflector.new
     @logger                     = self.class.default_logger
-    @manual_incepted_namespaces = []
+    @manual_incepted_namespaces = Set.new
     @tag                        = SecureRandom.hex(3)
     @initialized_at             = Time.now
     @roots                      = {}