Add memoize option for per-instance caching of deserialized values

When `memoize: true` is passed to `cacheable`, repeated calls on the
same instance skip the cache adapter entirely and return the previously
deserialized result. This avoids expensive repeated deserialization for
objects like ActiveRecord models. Memoized values are cleared by
`clear_*_cache` and garbage collected with the instance.

Closes #15

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: agrberg

README.md

@@ -254,6 +254,52 @@ If your cache backend supports options, you can pass them as the `cache_options:
 cacheable :with_options, cache_options: {expires_in: 3_600}
 ```
 
+### Memoization
+
+By default, every call to a cached method hits the cache adapter, which includes deserialization. For methods where the deserialized object is expensive to reconstruct (e.g., large ActiveRecord collections), you can enable per-instance memoization so that repeated calls on the **same object** skip the adapter entirely:
+
+```ruby
+# From examples/memoize_example.rb
+
+class ExpensiveService
+  include Cacheable
+
+  cacheable :without_memoize
+
+  cacheable :with_memoize, memoize: true
+
+  def without_memoize
+    puts '  [method] computing value'
+    42
+  end
+
+  def with_memoize
+    puts '  [method] computing value'
+    42
+  end
+end
+```
+
+Using a logging adapter wrapper (see `examples/memoize_example.rb` for the full setup), the difference becomes clear:
+
+```
+--- without memoize ---
+  [cache] fetch ["ExpensiveService", :without_memoize]
+  [method] computing value
+  [cache] fetch ["ExpensiveService", :without_memoize]    <-- adapter hit again (deserialization cost)
+
+--- with memoize: true ---
+  [cache] fetch ["ExpensiveService", :with_memoize]
+  [method] computing value
+                                                           <-- no adapter hit on second call
+
+--- after clearing ---
+  [cache] fetch ["ExpensiveService", :with_memoize]       <-- adapter hit again after clear
+  [method] computing value
+```
+
+**Important**: Memoized values persist for the lifetime of the object instance. If your cache key changes (e.g., `cache_key` based on `updated_at`), the memoized value will **not** automatically update. Use `memoize: true` only when you know the value will not change for the lifetime of the instance, or call `clear_#{method}_cache` explicitly when needed.
+
 ### Per-Class Cache Adapter
 
 By default, all classes use the global adapter set via `Cacheable.cache_adapter`. If you need a specific class to use a different cache backend, you can set one directly on the class:

examples/memoize_example.rb

@@ -0,0 +1,54 @@
+require 'cacheable' # this may not be necessary depending on your autoloading system
+
+# Wrap the default adapter to log cache reads
+logging_adapter = Cacheable::CacheAdapters::MemoryAdapter.new
+original_fetch = logging_adapter.method(:fetch)
+logging_adapter.define_singleton_method(:fetch) do |key, *args, &block|
+  puts "  [cache] fetch #{key.inspect}"
+  original_fetch.call(key, *args, &block)
+end
+
+Cacheable.cache_adapter = logging_adapter
+
+class ExpensiveService
+  include Cacheable
+
+  cacheable :without_memoize
+
+  cacheable :with_memoize, memoize: true
+
+  def without_memoize
+    puts '  [method] computing value'
+    42
+  end
+
+  def with_memoize
+    puts '  [method] computing value'
+    42
+  end
+end
+
+svc = ExpensiveService.new
+
+puts '--- without memoize ---'
+2.times { svc.without_memoize }
+# --- without memoize ---
+#   [cache] fetch ["ExpensiveService", :without_memoize]
+#   [method] computing value
+#   [cache] fetch ["ExpensiveService", :without_memoize]    <-- adapter hit again (deserialization cost)
+
+puts
+puts '--- with memoize: true ---'
+2.times { svc.with_memoize }
+# --- with memoize: true ---
+#   [cache] fetch ["ExpensiveService", :with_memoize]
+#   [method] computing value
+#                                                            <-- no adapter hit, returned from instance memo
+
+puts
+puts '--- after clearing ---'
+svc.clear_with_memoize_cache
+svc.with_memoize
+# --- after clearing ---
+#   [cache] fetch ["ExpensiveService", :with_memoize]
+#   [method] computing value

lib/cacheable.rb

@@ -31,6 +31,9 @@
 module Cacheable
   extend CacheAdapter
 
+  # Sentinel value to distinguish "not yet memoized" from a memoized nil/false.
+  MEMOIZE_NOT_SET = Object.new.freeze
+
   def self.included(base)
     base.extend(Cacheable::CacheAdapter)
     base.extend(Cacheable::MethodGenerator)

lib/cacheable/method_generator.rb

@@ -15,7 +15,7 @@ def method_interceptor_module_name
       "#{class_name}Cacher"
     end
 
-    # rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/MethodLength, Metrics/PerceivedComplexity
+    # rubocop:disable Metrics/AbcSize, Metrics/BlockLength, Metrics/CyclomaticComplexity, Metrics/MethodLength, Metrics/PerceivedComplexity
     def create_cacheable_methods(original_method_name, opts = {})
       method_names = create_method_names(original_method_name)
       key_format_proc = opts[:key_format] || default_key_format
@@ -28,6 +28,7 @@ def create_cacheable_methods(original_method_name, opts = {})
         end
 
         define_method(method_names[:clear_cache_method_name]) do |*args, **kwargs|
+          @_cacheable_memoized&.delete(original_method_name) if opts[:memoize]
           adapter = (is_a?(Module) ? singleton_class : self.class).cache_adapter
           adapter.delete(__send__(method_names[:key_format_method_name], *args, **kwargs))
         end
@@ -37,10 +38,20 @@ def create_cacheable_methods(original_method_name, opts = {})
         end
 
         define_method(method_names[:with_cache_method_name]) do |*args, **kwargs, &block|
+          cache_key = __send__(method_names[:key_format_method_name], *args, **kwargs)
+
+          if opts[:memoize]
+            method_memo = ((@_cacheable_memoized ||= {})[original_method_name] ||= {})
+            cached = method_memo.fetch(cache_key, Cacheable::MEMOIZE_NOT_SET)
+            return cached unless cached.equal?(Cacheable::MEMOIZE_NOT_SET)
+          end
+
           adapter = (is_a?(Module) ? singleton_class : self.class).cache_adapter
-          adapter.fetch(__send__(method_names[:key_format_method_name], *args, **kwargs), opts[:cache_options]) do # rubocop:disable Lint/UselessDefaultValueArgument -- not Hash#fetch; second arg is cache options (e.g. expires_in) passed to the adapter
+          result = adapter.fetch(cache_key, opts[:cache_options]) do # rubocop:disable Lint/UselessDefaultValueArgument -- not Hash#fetch; second arg is cache options (e.g. expires_in) passed to the adapter
             __send__(method_names[:without_cache_method_name], *args, **kwargs, &block)
           end
+          method_memo[cache_key] = result if opts[:memoize]
+          result
         end
 
         define_method(original_method_name) do |*args, **kwargs, &block|
@@ -52,7 +63,7 @@ def create_cacheable_methods(original_method_name, opts = {})
         end
       end
     end
-    # rubocop:enable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/MethodLength, Metrics/PerceivedComplexity
+    # rubocop:enable Metrics/AbcSize, Metrics/BlockLength, Metrics/CyclomaticComplexity, Metrics/MethodLength, Metrics/PerceivedComplexity
 
     def default_key_format
       warned = false

spec/cacheable/cacheable_spec.rb

@@ -598,4 +598,166 @@ def cache_control_method
     expect(described_class.cache_adapter).to receive(:fetch).with(anything, hash_including(cache_options))
     cacheable_object.send(cache_method_with_cache_options)
   end
+
+  describe 'memoization' do
+    let(:class_definition) do
+      cacheable_method_name = cacheable_method
+      cacheable_method_inner_name = cacheable_method_inner
+      mod = described_class
+      proc do
+        include mod
+
+        define_method(cacheable_method_name) do |arg = nil|
+          send cacheable_method_inner_name, arg
+        end
+
+        define_method(cacheable_method_inner_name) do |arg = nil|
+          "a unique value with arg #{arg}"
+        end
+
+        cacheable cacheable_method_name, memoize: true
+      end
+    end
+
+    it 'returns the expected value' do
+      expect(cacheable_object.send(cacheable_method)).to eq(cacheable_object.send(cacheable_method_inner))
+    end
+
+    it 'only hits the cache adapter once for repeated calls' do
+      adapter = described_class.cache_adapter
+      expect(adapter).to receive(:fetch).once.and_call_original
+
+      2.times { cacheable_object.send(cacheable_method) }
+    end
+
+    it 'different instances have independent memoization' do
+      obj1 = cacheable_class.new
+      obj2 = cacheable_class.new
+
+      obj1.send(cacheable_method)
+      obj2.send(cacheable_method)
+
+      # Each should have its own memo store
+      expect(obj1.instance_variable_get(:@_cacheable_memoized)).not_to be(obj2.instance_variable_get(:@_cacheable_memoized))
+    end
+
+    it 'memoizes different arguments independently when key_format includes args' do
+      args_method = :args_memoize_method
+      inner_method = cacheable_method_inner
+      cacheable_class.class_eval do
+        define_method(args_method) do |arg|
+          send inner_method, arg
+        end
+
+        cacheable args_method, memoize: true, key_format: proc { |target, method_name, method_args|
+          [target.class, method_name, method_args]
+        }
+      end
+
+      adapter = described_class.cache_adapter
+      expect(adapter).to receive(:fetch).twice.and_call_original
+
+      2.times { cacheable_object.send(args_method, 'arg1') }
+      2.times { cacheable_object.send(args_method, 'arg2') }
+    end
+
+    it 'clears memoized value when clear_cache is called' do
+      adapter = described_class.cache_adapter
+      expect(adapter).to receive(:fetch).twice.and_call_original
+
+      cacheable_object.send(cacheable_method)
+      cacheable_object.send("clear_#{cacheable_method}_cache")
+      cacheable_object.send(cacheable_method)
+    end
+
+    it 'does not memoize when unless proc is true' do
+      skip_method = :skip_memoize_method
+      inner_method = cacheable_method_inner
+      cacheable_class.class_eval do
+        define_method(skip_method) do
+          send inner_method
+        end
+
+        cacheable skip_method, memoize: true, unless: proc { true }
+      end
+
+      expect(cacheable_object).to receive(inner_method).twice.and_call_original
+      2.times { cacheable_object.send(skip_method) }
+    end
+
+    it 'memoizes nil return values' do
+      nil_method = :nil_memoize_method
+      call_count = 0
+      cacheable_class.class_eval do
+        define_method(nil_method) do
+          call_count += 1
+          nil
+        end
+
+        cacheable nil_method, memoize: true
+      end
+
+      2.times { cacheable_object.send(nil_method) }
+      expect(call_count).to eq(1)
+    end
+
+    it 'memoizes false return values' do
+      false_method = :false_memoize_method
+      call_count = 0
+      cacheable_class.class_eval do
+        define_method(false_method) do
+          call_count += 1
+          false
+        end
+
+        cacheable false_method, memoize: true
+      end
+
+      2.times { cacheable_object.send(false_method) }
+      expect(call_count).to eq(1)
+    end
+
+    it 'does not set @_cacheable_memoized when memoize is not used' do
+      non_memo_class = Class.new.tap do |klass|
+        klass.class_exec do
+          include Cacheable
+
+          def some_method
+            'value'
+          end
+
+          cacheable :some_method
+        end
+      end
+
+      obj = non_memo_class.new
+      obj.some_method
+      expect(obj.instance_variable_defined?(:@_cacheable_memoized)).to be false
+    end
+
+    it 'passes cache_options to the adapter on the first call' do
+      opts_method = :opts_memoize_method
+      cache_options = {expires_in: 3_600}
+      cacheable_class.class_eval do
+        define_method(opts_method) { 'value' }
+        cacheable opts_method, memoize: true, cache_options: cache_options
+      end
+
+      expect(described_class.cache_adapter).to receive(:fetch).with(anything, hash_including(cache_options)).once.and_call_original
+      2.times { cacheable_object.send(opts_method) }
+    end
+
+    context 'with class methods' do
+      let(:cacheable_class) do
+        Class.new.tap { |klass| klass.singleton_class.class_exec(&class_definition) }
+      end
+
+      it 'memoizes class method calls' do
+        adapter = described_class.cache_adapter
+        expect(adapter).to receive(:fetch).once.and_call_original
+
+        2.times { cacheable_class.send(cacheable_method) }
+      end
+    end
+  end
 end