Allow pattern matching solely against a result's data (#20)

README.md

@@ -70,7 +70,7 @@ end
 
 ## Pattern matching
 
-An Operatic result also supports pattern matching in Ruby 2.7+ returning an array of `[success, data]`:
+An Operatic result also supports pattern matching allowing you to match over a tuple of the result class and its data:
 
 ```ruby
 case SayHello.call(name: 'Dave')
@@ -81,6 +81,17 @@ in [Operatic::Failure, _]
 end
 ```
 
+Or match solely against its data:
+
+```ruby
+case SayHello.call(name: 'Dave')
+in message:
+  # Result has the `message` key, do something with the variable.
+else
+  # Do something else.
+end
+```
+
 Which might be consumed in Rails like this:
 
 ```ruby

lib/operatic/result.rb

@@ -41,6 +41,29 @@ def deconstruct
       [self, to_h]
     end
 
+    # Pattern match against the result's data via {#to_h}.
+    #
+    # @example
+    #   class SayHello
+    #     include Operatic
+    #
+    #     def call
+    #       data[:message] = 'Hello world'
+    #     end
+    #   end
+    #
+    #   case SayHello.call
+    #   in message:
+    #     # Result has the `message` key, do something with the variable.
+    #   else
+    #     # Do something else.
+    #   end
+    #
+    # @return [Hash<Symbol, anything>]
+    def deconstruct_keys(keys = nil)
+      to_h
+    end
+
     # @return [self]
     def freeze
       data.freeze

spec/lib/operatic/result_spec.rb

@@ -25,6 +25,21 @@
     end
   end
 
+  describe '#deconstruct_keys (pattern matching)' do
+    subject { described_class.new(data) }
+
+    let(:data) { Operatic::Data.new(a: 1, b: 2, c: 3) }
+
+    it 'matches against its data' do
+      deconstructed = case subject
+      in a:, c:
+        [a, c]
+      end
+
+      expect(deconstructed).to eql([1, 3])
+    end
+  end
+
   describe '#method_missing / #respond_to?' do
     subject { described_class.new(data) }