Fix pattern matching

features/advanced/pattern_matching.feature

@@ -0,0 +1,133 @@
+Feature: Method Overloading
+
+  You can use contracts for method overloading! This is commonly called "pattern matching" in functional programming languages.
+
+  ```ruby
+  Contract 1 => 1
+  def fact x
+    x
+  end
+
+  Contract C::Num => C::Num
+  def fact x
+    x * fact(x - 1)
+  end
+  ```
+
+  Background:
+    Given a file named "method_overloading_with_positional_args_usage.rb" with:
+    """ruby
+    require "contracts"
+    C = Contracts
+
+    class Example
+      include Contracts::Core
+
+      Contract 1 => 1
+      def fact(x)
+        x
+      end
+
+      Contract C::Num => C::Num
+      def fact(x)
+        x * fact(x - 1)
+      end
+    end
+    """
+
+    Given a file named "method_overloading_with_keyword_args_usage.rb" with:
+    """ruby
+    require "contracts"
+    C = Contracts
+
+    class Example
+      include Contracts::Core
+
+      Contract C::KeywordArgs[age: Integer, size: Symbol] => String
+      def speak(age:, size:)
+        "age: #{age} size: #{size}"
+      end
+
+      Contract C::KeywordArgs[sound: String] => String
+      def speak(sound:)
+        "sound: #{sound}"
+      end
+    end
+    """
+
+  Scenario: Positional Args Method 1
+    Given a file named "positional_args_method_1.rb" with:
+    """ruby
+    require "./method_overloading_with_positional_args_usage"
+    puts Example.new.fact(1)
+    """
+    When I run `ruby positional_args_method_1.rb`
+    Then the output should contain:
+    """
+    1
+    """
+
+  Scenario: Positional Args Method 2
+    Given a file named "positional_args_method_2.rb" with:
+    """ruby
+    require "./method_overloading_with_positional_args_usage"
+    puts Example.new.fact(4)
+    """
+    When I run `ruby positional_args_method_2.rb`
+    Then the output should contain:
+    """
+    24
+    """
+
+  Scenario: Keyword Args Method 1
+    Given a file named "keyword_args_method_1.rb" with:
+    """ruby
+    require "./method_overloading_with_keyword_args_usage"
+    puts Example.new.speak(age: 5, size: :large)
+    """
+    When I run `ruby keyword_args_method_1.rb`
+    Then the output should contain:
+    """
+    age: 5 size: large
+    """
+
+  Scenario: Keyword Args Method 2
+    Given a file named "keyword_args_method_2.rb" with:
+    """ruby
+    require "./method_overloading_with_keyword_args_usage"
+    puts Example.new.speak(sound: "woof")
+    """
+    When I run `ruby keyword_args_method_2.rb`
+    Then the output should contain:
+    """
+    sound: woof
+    """
+
+  Scenario: Incorrect Positional Args Method
+    Given a file named "incorrect_positional_args_method.rb" with:
+    """ruby
+    require "contracts"
+    C = Contracts
+
+    class Example
+      include Contracts::Core
+
+      # Notice that this method's contract is wider than the one below
+      # This would cause this method to be called every time but never the one below
+      Contract C::Num => C::Num
+      def fact(x)
+        x * fact(x - 1)
+      end
+
+      Contract 1 => 1
+      def fact(x)
+        x
+      end
+    end
+    puts Example.new.fact(4)
+    """
+    When I run `ruby incorrect_positional_args_method.rb`
+    Then the output should contain:
+    """
+    stack level too deep (SystemStackError)
+    """

lib/contracts/method_handler.rb

@@ -174,8 +174,10 @@ def foo x
 
     def validate_pattern_matching!
       new_args_contract = decorator.args_contracts
+      new_kargs_contract = decorator.kargs_contract
       matched = decorated_methods.select do |contract|
-        contract.args_contracts == new_args_contract
+        contract.args_contracts == new_args_contract &&
+          contract.kargs_contract == new_kargs_contract
       end
 
       return if matched.empty?