Replace methods by singleton_methods when overriding them.

Author: ericproulx

CHANGELOG.md

@@ -10,6 +10,7 @@
 * [#2581](https://github.com/ruby-grape/grape/pull/2581): Delegate `to_s` in Grape::API::Instance - [@ericproulx](https://github.com/ericproulx).
 * [#2582](https://github.com/ruby-grape/grape/pull/2582): Fix leaky slash when normalizing - [@ericproulx](https://github.com/ericproulx).
 * [#2583](https://github.com/ruby-grape/grape/pull/2583): Optimize api parameter documentation and memory usage - [@ericproulx](https://github.com/ericproulx).
+* [#2585](https://github.com/ruby-grape/grape/pull/2585): Optimize mount methods overriding - [@ericproulx](https://github.com/ericproulx).
 * Your contribution here.
 
 #### Fixes

lib/grape/api.rb

@@ -5,7 +5,7 @@ module Grape
   # should subclass this class in order to build an API.
   class API
     # Class methods that we want to call on the API rather than on the API object
-    NON_OVERRIDABLE = %i[call call! configuration compile! inherited recognize_path].freeze
+    NON_OVERRIDABLE = %i[call call! configuration compile! inherited recognize_path to_s].freeze
 
     Helpers = Grape::DSL::Helpers::BaseHelper
 
@@ -51,7 +51,7 @@ def initial_setup(base_instance_parent)
 
       # Redefines all methods so that are forwarded to add_setup and be recorded
       def override_all_methods!
-        (base_instance.methods - Class.methods - NON_OVERRIDABLE).each do |method_override|
+        (base_instance.singleton_methods - NON_OVERRIDABLE).each do |method_override|
           define_singleton_method(method_override) do |*args, &block|
             add_setup(method: method_override, args: args, block: block)
           end