Add ReferenceMatcher type

src/spectator/matchers/reference_matcher.cr

@@ -0,0 +1,47 @@
+require "./value_matcher"
+
+module Spectator::Matchers
+  # Matcher that tests whether two references are the same.
+  # The values are compared with the `Reference#same?` method.
+  struct ReferenceMatcher(ExpectedType) < ValueMatcher(ExpectedType)
+    # Determines whether the matcher is satisfied with the value given to it.
+    private def match?(actual)
+      actual.same?(expected)
+    end
+
+    # Determines whether the matcher is satisfied with the partial given to it.
+    # `MatchData` is returned that contains information about the match.
+    def match(partial)
+      values = ExpectedActual.new(partial, self)
+      MatchData.new(match?(values.actual), values)
+    end
+
+    # Match data specific to this matcher.
+    private struct MatchData(ExpectedType, ActualType) < MatchData
+      # Creates the match data.
+      def initialize(matched, @values : ExpectedActual(ExpectedType, ActualType))
+        super(matched)
+      end
+
+      # Information about the match.
+      def named_tuple
+        {
+          expected: NegatableMatchDataValue.new(@values.expected),
+          actual:   @values.actual,
+        }
+      end
+
+      # Describes the condition that satisfies the matcher.
+      # This is informational and displayed to the end-user.
+      def message
+        "#{@values.actual_label} is #{@values.expected_label}"
+      end
+
+      # Describes the condition that won't satsify the matcher.
+      # This is informational and displayed to the end-user.
+      def negated_message
+        "#{@values.actual_label} is not #{@values.expected_label}"
+      end
+    end
+  end
+end