JoelQ · September 23, 2024 03:02 · Apr 6, 2022 · Apr 6, 2022
diff --git a/value_object_shared_examples.rb b/value_object_shared_examples.rb
@@ -0,0 +1,41 @@
+RSpec.shared_examples_for "value object" do
+  describe "#hash" do
+    it "is the same as another instance of the same value" do
+      expect(item.hash).to eq same.hash
+    end
+
+    it "is the different from another instance of a different value" do
+      expect(item.hash).not_to eq different.hash
+    end
+  end
+
+  describe "#eql?" do
+    it "two instances are eql if they have the same value" do
+      expect(item).to be_eql same
+    end
+
+    it "two instances are not eql if they have a different value" do
+      expect(item).not_to be_eql different
+    end
+  end
+
+  describe "#==" do
+    it "two instances are == if they have the same value" do
+      expect(item).to eq same
+    end
+
+    it "two instances are not == if they have a different value" do
+      expect(item).not_to eq different
+    end
+  end
+
+  describe "#equal?" do
+    it "is equal if two object share the same identity" do
+      expect(item).to be_equal item
+    end
+
+    it "is not equal if two different objects share the same value" do
+      expect(item).not_to be_equal same
+    end
+  end
+end
diff --git a/dollar.rb b/dollar.rb
@@ -0,0 +1,16 @@
+class Dollar
+  attr_reader :cents
+
+  def initialize(cents:)
+    @cents = cents
+  end
+
+  def hash
+    [self.class, cents].hash
+  end
+
+  def ==(other)
+    cents == other.cents
+  end
+  alias_method :eql?, :==
+end
diff --git a/dollar_spec.rb b/dollar_spec.rb
@@ -0,0 +1,10 @@
+require_relative "dollar"
+require_relative "value_object_shared_examples"
+
+RSpec.describe Dollar do
+  it_behaves_like "value object" do
+    let(:item) { Dollar.new(cents: 5) }
+    let(:same) { Dollar.new(cents: 5) }
+    let(:different) { Dollar.new(cents: 10) }
+  end
+end
diff --git a/duration.rb b/duration.rb
@@ -0,0 +1,16 @@
+class Duration
+  attr_reader :milliseconds
+
+  def initialize(milliseconds:)
+    @milliseconds = milliseconds
+  end
+
+  def hash
+    [self.class, milliseconds].hash
+  end
+
+  def ==(other)
+    milliseconds == other.milliseconds
+  end
+  alias_method :eql?, :==
+end
diff --git a/duration_spec.rb b/duration_spec.rb
@@ -0,0 +1,10 @@
+require_relative "duration"
+require_relative "value_object_shared_examples"
+
+RSpec.describe Duration do
+  it_behaves_like "value object" do
+    let(:item) { Duration.new(milliseconds: 1000) }
+    let(:same) { Duration.new(milliseconds: 1000) }
+    let(:different) { Duration.new(milliseconds: 1234) }
+  end
+end
diff --git a/shell_output.log b/shell_output.log
@@ -0,0 +1,38 @@
+ % rspec duration_spec.rb dollar_spec.rb --format documentation
+
+Randomized with seed 9567
+
+Dollar
+  behaves like value object
+    #==
+      two instances are not == if they have a different value
+      two instances are == if they have the same value
+    #hash
+      is the same as another instance of the same value
+      is the different from another instance of a different value
+    #equal?
+      is equal if two object share the same identity
+      is not equal if two different objects share the same value
+    #eql?
+      two instances are not eql if they have a different value
+      two instances are eql if they have the same value
+
+Duration
+  behaves like value object
+    #==
+      two instances are == if they have the same value
+      two instances are not == if they have a different value
+    #hash
+      is the same as another instance of the same value
+      is the different from another instance of a different value
+    #eql?
+      two instances are eql if they have the same value
+      two instances are not eql if they have a different value
+    #equal?
+      is not equal if two different objects share the same value
+      is equal if two object share the same identity
+
+Finished in 0.00453 seconds (files took 0.11736 seconds to load)
+16 examples, 0 failures
+
+Randomized with seed 9567
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