Mix ActiveModel::AttributeMethods into ActiveResource::Base

[seanpdoyle]

The problem

The current attribute reading and writing implementation relies upon #method_missing and #respond_to_missing? for access.

When attributes are defined by a schema, it's possible to define methods for them at "declaration time", rather than implementing access entirely through method missing reflection.

The solution

Mix ActiveModel::AttributeMethods into ActiveResource::Base, then hook into schema assignment. When assigning attributes, invoke define_attribute_methods. When the schema is reset to be nil, invoke undefine_attribute_methods.

[rafaelfranca]

Do you have benchmarks to show if this change changed the performance of reading and writing attributes?

[seanpdoyle]

@rafaelfranca after making the following benchmark-related changes:

diff --git a/lib/active_resource/base.rb b/lib/active_resource/base.rb
index e34714e..f43675d 100644
--- a/lib/active_resource/base.rb
+++ b/lib/active_resource/base.rb
@@ -371,6 +371,7 @@ module ActiveResource
       @@logger = logger
     end
 
+    class_attribute :define_methods, default: true
     class_attribute :lazy_collections, default: true, instance_accessor: false
     class_attribute :_query_format
     class_attribute :_format
@@ -463,7 +464,7 @@ module ActiveResource
             @schema[k] = v
             @known_attributes << k
           end
-          define_attribute_methods @known_attributes
+          define_attribute_methods(@known_attributes) if define_methods
 
           @schema
         else
@@ -493,7 +494,7 @@ module ActiveResource
           # purposefully nulling out the schema
           @schema = nil
           @known_attributes = []
-          undefine_attribute_methods
+          undefine_attribute_methods if define_methods
           return
         end

I executed the following script:

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  gem "activeresource", path: "."
  gem "benchmark-ips"
end

class WithAttributeMethods < ActiveResource::Base
  self.define_methods = true

  schema do
    attribute :known, :string
  end
end

class WithoutAttributeMethods < ActiveResource::Base
  self.define_methods = false

  schema do
    attribute :known, :string
  end
end

require "benchmark/ips"

Benchmark.ips do |x|
  x.report("with") do |n|
    with = WithAttributeMethods.new

    n.times do
      with.known = "value"
      with.known
      with.unknown = "value"
      with.unknown
    end
  end

  x.report("without") do |n|
    without = WithoutAttributeMethods.new

    n.times do
      without.known = "value"
      without.known
      without.unknown = "value"
      without.unknown
    end
  end

  x.compare!
end

The with is code for this branch's changes, the without is code prior to the proposed changes.

❯ ruby benchmark.rb 
Fetching gem metadata from https://rubygems.org/........
Resolving dependencies...
ruby 3.4.5 (2025-07-16 revision 20cda200d3) +PRISM [arm64-darwin24]
Warming up --------------------------------------
                with    51.419k i/100ms
             without    41.498k i/100ms
Calculating -------------------------------------
                with    513.968k (± 1.1%) i/s    (1.95 μs/i) -      2.571M in   5.002721s
             without    415.405k (± 1.1%) i/s    (2.41 μs/i) -      2.116M in   5.095418s

Comparison:
                with:   513968.3 i/s
             without:   415404.6 i/s - 1.24x  slower

While improving performance (or at least not hindering performance) is one motivation, this change is also required for the ActiveModel::Dirty integration proposed in #466 (and improves ActiveModel::Attributes-compliance explored in #410).