Merge pull request #12 from nicheinc/feature/apply-ptr

Add ApplyPtr and DiffPtr methods to Update[T]
nicheinc · Aug 25, 2022 · b70bdfc · b70bdfc
2 parents 20c4b70 + c7e0404
commit b70bdfc
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Showing 3 changed files with 132 additions and 5 deletions.
diff --git a/nup/sliceUpdate_test.go b/nup/sliceUpdate_test.go
@@ -51,7 +51,7 @@ func TestSliceUpdate_UnmarshalJSON(t *testing.T) {
 			if err := json.Unmarshal([]byte(testCase.json), &dst); err != nil {
 				t.Errorf("Error unmarshaling JSON: %s", err)
 			}
-			if !reflect.DeepEqual(dst.Update, testCase.expected) {
+			if !dst.Update.Equal(testCase.expected) {
 				t.Errorf("Expected: %v. Actual: %v", testCase.expected, dst.Update)
 			}
 		})
@@ -84,7 +84,7 @@ func TestSliceRemoveOrSet(t *testing.T) {
 	for _, testCase := range testCases {
 		t.Run(testCase.name, func(t *testing.T) {
 			actual := SliceRemoveOrSet(testCase.value)
-			if !reflect.DeepEqual(actual, testCase.expected) {
+			if !actual.Equal(testCase.expected) {
 				t.Errorf("Expected: %v. Actual: %v", testCase.expected, actual)
 			}
 		})

diff --git a/nup/update.go b/nup/update.go
@@ -116,6 +116,22 @@ func (u Update[T]) Apply(value T) T {
 	}
 }
 
+// ApplyPtr returns the result of applying the update to the given pointer
+// value. The result is the given value if the update is a no-op, nil if it's a
+// removal, or a copy of the update's contained value if it's a set operation.
+func (u Update[T]) ApplyPtr(value *T) *T {
+	switch u.op {
+	case OpNoop:
+		return value
+	case OpRemove:
+		return nil
+	default: // Set
+		// Copy the update value so it can't be mutated via the returned pointer.
+		value := u.value
+		return &value
+	}
+}
+
 // Diff returns the update itself if Apply(value) != value; otherwise it returns
 // a no-op update. Diff can be used to omit extraneous updates when applying
 // them would have no effect.
@@ -126,6 +142,22 @@ func (u Update[T]) Diff(value T) Update[T] {
 	return u
 }
 
+// DiffPtr returns the update itself if ApplyPtr(value) does not contain a value
+// equal to the given value; otherwise it returns a no-op update. DiffPtr can be
+// used to omit extraneous updates when applying them would have no effect.
+func (u Update[T]) DiffPtr(value *T) Update[T] {
+	applied := u.ApplyPtr(value)
+	switch {
+	case applied == nil && value == nil:
+		return Noop[T]()
+	case applied == nil || value == nil:
+		return u
+	default:
+		return u.Diff(*value)
+	}
+
+}
+
 // UnmarshalJSON implements json.Unmarshaler.
 func (u *Update[T]) UnmarshalJSON(data []byte) error {
 	if string(data) == "null" {

diff --git a/nup/update_test.go b/nup/update_test.go
@@ -43,7 +43,7 @@ func TestUpdate_UnmarshalJSON(t *testing.T) {
 			if err := json.Unmarshal([]byte(testCase.json), &dst); err != nil {
 				t.Errorf("Error unmarshaling JSON: %s", err)
 			}
-			if !reflect.DeepEqual(dst.Update, testCase.expected) {
+			if dst.Update != testCase.expected {
 				t.Errorf("Expected: %v. Actual: %v", testCase.expected, dst.Update)
 			}
 		})
@@ -293,6 +293,42 @@ func TestUpdate_Apply(t *testing.T) {
 	}
 }
 
+func TestUpdate_ApplyPtr(t *testing.T) {
+	var (
+		value1 = 1
+		value2 = 2
+	)
+	testCases := []struct {
+		name     string
+		update   Update[int]
+		expected *int
+	}{
+		{
+			name:     "Noop",
+			update:   Noop[int](),
+			expected: &value1,
+		},
+		{
+			name:     "Remove",
+			update:   Remove[int](),
+			expected: nil,
+		},
+		{
+			name:     "Set",
+			update:   Set(value2),
+			expected: &value2,
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			if actual := testCase.update.ApplyPtr(&value1); !reflect.DeepEqual(actual, testCase.expected) {
+				t.Errorf("Expected: %v. Actual: %v", testCase.expected, actual)
+			}
+		})
+	}
+}
+
 func TestUpdate_Diff(t *testing.T) {
 	var (
 		value1 = 1
@@ -319,7 +355,7 @@ func TestUpdate_Diff(t *testing.T) {
 		{
 			name:     "Remove/ZeroValue",
 			update:   Remove[int](),
-			value:    0.0,
+			value:    0,
 			expected: Noop[int](),
 		},
 		{
@@ -338,7 +374,66 @@ func TestUpdate_Diff(t *testing.T) {
 
 	for _, testCase := range testCases {
 		t.Run(testCase.name, func(t *testing.T) {
-			if actual := testCase.update.Diff(testCase.value); !reflect.DeepEqual(actual, testCase.expected) {
+			if actual := testCase.update.Diff(testCase.value); actual != testCase.expected {
+				t.Errorf("Expected: %v. Actual: %v", testCase.expected, actual)
+			}
+		})
+	}
+}
+
+func TestUpdate_DiffPtr(t *testing.T) {
+	var (
+		zero   = 0
+		value1 = 1
+		value2 = 2
+	)
+	testCases := []struct {
+		name     string
+		update   Update[int]
+		value    *int
+		expected Update[int]
+	}{
+		{
+			name:     "Noop",
+			update:   Noop[int](),
+			value:    &value1,
+			expected: Noop[int](),
+		},
+		{
+			name:     "Remove/ZeroValue",
+			update:   Remove[int](),
+			value:    &zero,
+			expected: Remove[int](),
+		},
+		{
+			name:     "Remove/NonZeroValue",
+			update:   Remove[int](),
+			value:    &value1,
+			expected: Remove[int](),
+		},
+		{
+			name:     "Remove/Nil",
+			update:   Remove[int](),
+			value:    nil,
+			expected: Noop[int](),
+		},
+		{
+			name:     "Set/Equal",
+			update:   Set(value1),
+			value:    &value1,
+			expected: Noop[int](),
+		},
+		{
+			name:     "Set/NotEqual",
+			update:   Set(value2),
+			value:    &value1,
+			expected: Set(value2),
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			if actual := testCase.update.DiffPtr(testCase.value); actual != testCase.expected {
 				t.Errorf("Expected: %v. Actual: %v", testCase.expected, actual)
 			}
 		})