contain_exactly should work with sets and other collections, too.

Changelog.md

@@ -22,6 +22,8 @@ Enhancements:
   Note that it expects the expected array to be splatted as
   individual args: `expect(array).to contain_exactly(1, 2)` is
   the same as `expect(array).to match_array([1, 2])`. (Myron Marston)
+* Update `contain_exactly`/`match_array` so that it can match against
+  other non-array collections (such as a `Set`). (Myron Marston)
 * Update built-in matchers so that they can accept matchers as arguments
   to allow you to compose matchers in arbitrary ways. (Myron Marston)
 * Add `RSpec::Matchers::Composable` mixin that can be used to make

lib/rspec/matchers/built_in/contain_exactly.rb

@@ -3,21 +3,21 @@ module Matchers
     module BuiltIn
       class ContainExactly < BaseMatcher
         def match(expected, actual)
-          return false unless actual.respond_to? :to_ary
+          return false unless actual_is_a_collection?
+          @actual = actual.to_a
           extra_items.empty? && missing_items.empty?
         end
 
         def failure_message
-          if actual.respond_to? :to_ary
-            message =  "expected collection contained:  #{safe_sort(surface_descriptions_in expected).inspect}\n"
+          if actual_is_a_collection?
+            message  = "expected collection contained:  #{safe_sort(surface_descriptions_in expected).inspect}\n"
             message += "actual collection contained:    #{safe_sort(actual).inspect}\n"
             message += "the missing elements were:      #{safe_sort(surface_descriptions_in missing_items).inspect}\n" unless missing_items.empty?
             message += "the extra elements were:        #{safe_sort(extra_items).inspect}\n" unless extra_items.empty?
+            message
           else
-            message = "expected an array, actual collection was #{actual.inspect}"
+            "expected a collection that can be converted to an array with `#to_a`, but got #{actual.inspect}"
           end
-
-          message
         end
 
         def failure_message_when_negated
@@ -30,6 +30,10 @@ def description
 
       private
 
+        def actual_is_a_collection?
+          enumerable?(actual) && actual.respond_to?(:to_a)
+        end
+
         def safe_sort(array)
           array.sort rescue array
         end

spec/rspec/matchers/built_in/contain_exactly_spec.rb

@@ -189,27 +189,26 @@ def timeout_if_not_debugging(time)
   it "fails with nil and the expected error message is given" do
     expect {
       expect(nil).to contain_exactly(1, 2, 3)
-    }.to fail_with(/expected an array/)
+    }.to fail_with(/expected a collection/)
   end
 
   it "fails with a float and the expected error message is given" do
     expect {
       expect(3.7).to contain_exactly(1, 2, 3)
-    }.to fail_with(/expected an array/)
+    }.to fail_with(/expected a collection/)
   end
 
   it "fails with a string and the expected error message is given" do
     expect {
       expect("I like turtles").to contain_exactly(1, 2, 3)
-    }.to fail_with(/expected an array/)
+    }.to fail_with(/expected a collection/)
   end
 
-  context "when using the `should =~` syntax", :uses_should do
-    it 'fails with a clear message when given a hash' do
-      expect {
-        {}.should =~ {}
-      }.to fail_with(/expected an array/)
-    end
+  it 'works with other collection types' do
+    expect(Set.new([3, 2, 1])).to contain_exactly(1, 2, 3)
+    expect {
+      expect(Set.new([3, 2, 1])).to contain_exactly(1, 2)
+    }.to fail_matching("expected collection contained:  [1, 2]")
   end
 end