stop memoizing result of HaveField

fixes #787

Author: onsi

matchers/have_field.go

@@ -17,7 +17,7 @@ func (e missingFieldError) Error() string {
 	return string(e)
 }
 
-func extractField(actual interface{}, field string, matchername string) (interface{}, error) {
+func extractField(actual interface{}, field string, matchername string) (any, error) {
 	fields := strings.SplitN(field, ".", 2)
 	actualValue := reflect.ValueOf(actual)
 
@@ -64,36 +64,46 @@ func extractField(actual interface{}, field string, matchername string) (interfa
 type HaveFieldMatcher struct {
 	Field    string
 	Expected interface{}
+}
 
-	extractedField  interface{}
-	expectedMatcher omegaMatcher
+func (matcher *HaveFieldMatcher) expectedMatcher() omegaMatcher {
+	var isMatcher bool
+	expectedMatcher, isMatcher := matcher.Expected.(omegaMatcher)
+	if !isMatcher {
+		expectedMatcher = &EqualMatcher{Expected: matcher.Expected}
+	}
+	return expectedMatcher
 }
 
 func (matcher *HaveFieldMatcher) Match(actual interface{}) (success bool, err error) {
-	matcher.extractedField, err = extractField(actual, matcher.Field, "HaveField")
+	extractedField, err := extractField(actual, matcher.Field, "HaveField")
 	if err != nil {
 		return false, err
 	}
 
-	var isMatcher bool
-	matcher.expectedMatcher, isMatcher = matcher.Expected.(omegaMatcher)
-	if !isMatcher {
-		matcher.expectedMatcher = &EqualMatcher{Expected: matcher.Expected}
-	}
-
-	return matcher.expectedMatcher.Match(matcher.extractedField)
+	return matcher.expectedMatcher().Match(extractedField)
 }
 
 func (matcher *HaveFieldMatcher) FailureMessage(actual interface{}) (message string) {
+	extractedField, err := extractField(actual, matcher.Field, "HaveField")
+	if err != nil {
+		// this really shouldn't happen
+		return fmt.Sprintf("Failed to extract field '%s': %s", matcher.Field, err)
+	}
 	message = fmt.Sprintf("Value for field '%s' failed to satisfy matcher.\n", matcher.Field)
-	message += matcher.expectedMatcher.FailureMessage(matcher.extractedField)
+	message += matcher.expectedMatcher().FailureMessage(extractedField)
 
 	return message
 }
 
 func (matcher *HaveFieldMatcher) NegatedFailureMessage(actual interface{}) (message string) {
+	extractedField, err := extractField(actual, matcher.Field, "HaveField")
+	if err != nil {
+		// this really shouldn't happen
+		return fmt.Sprintf("Failed to extract field '%s': %s", matcher.Field, err)
+	}
 	message = fmt.Sprintf("Value for field '%s' satisfied matcher, but should not have.\n", matcher.Field)
-	message += matcher.expectedMatcher.NegatedFailureMessage(matcher.extractedField)
+	message += matcher.expectedMatcher().NegatedFailureMessage(extractedField)
 
 	return message
 }

matchers/have_field_test.go

@@ -140,15 +140,17 @@ var _ = Describe("HaveField", func() {
 	})
 
 	Describe("Failure Messages", func() {
-		It("renders the underlying matcher failure", func() {
+		It("renders the underlying matcher failure without caching the object", func() {
 			matcher := HaveField("Title", "Les Mis")
 			success, err := matcher.Match(book)
 			Ω(success).Should(BeFalse())
 			Ω(err).ShouldNot(HaveOccurred())
 
+			book.Title = "Les Miser"
 			msg := matcher.FailureMessage(book)
-			Ω(msg).Should(Equal("Value for field 'Title' failed to satisfy matcher.\nExpected\n    <string>: Les Miserables\nto equal\n    <string>: Les Mis"))
+			Ω(msg).Should(Equal("Value for field 'Title' failed to satisfy matcher.\nExpected\n    <string>: Les Miser\nto equal\n    <string>: Les Mis"))
 
+			book.Title = "Les Miserables"
 			matcher = HaveField("Title", "Les Miserables")
 			success, err = matcher.Match(book)
 			Ω(success).Should(BeTrue())