Merge pull request #8 from nyaruka/generic_map

Convert `null.Map` to be generic

.github/workflows/ci.yml

@@ -6,11 +6,11 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: [1.19.x, 1.20.x]
+        go-version: [1.19.x, 1.20.x, 1.21.x]
 
     services:
       postgres:
-        image: postgis/postgis:14-3.3-alpine
+        image: postgis/postgis:15-3.3-alpine
         env:
           POSTGRES_DB: null_test
           POSTGRES_USER: null_test

README.md

@@ -14,7 +14,7 @@ you marshal the zero value to JSON, you will get `null`.
 | `null.Int`    | `int(0)`        
 | `null.Int64`  | `int64(0)`      
 | `null.String` | `""`            
-| `null.Map`    | `map[string]any{}`         
+| `null.Map[V]`    | `map[string]V{}`         
 | `null.JSON`   | `[]byte("null")`  
 
 If you want to define a custom integer type, you need to define the following methods:

map.go

@@ -7,24 +7,24 @@ import (
 )
 
 // Map is a generic map which is written to the database as JSON.
-type Map map[string]any
+type Map[V any] map[string]V
 
 // Scan implements the Scanner interface
-func (m *Map) Scan(value any) error { return ScanMap(value, m) }
+func (m *Map[V]) Scan(value any) error { return ScanMap(value, m) }
 
 // Value implements the Valuer interface
-func (m Map) Value() (driver.Value, error) { return MapValue(m) }
+func (m Map[V]) Value() (driver.Value, error) { return MapValue(m) }
 
 // UnmarshalJSON implements the Unmarshaller interface
-func (m *Map) UnmarshalJSON(data []byte) error { return UnmarshalMap(data, m) }
+func (m *Map[V]) UnmarshalJSON(data []byte) error { return UnmarshalMap(data, m) }
 
 // MarshalJSON implements the Marshaller interface
-func (m Map) MarshalJSON() ([]byte, error) { return MarshalMap(m) }
+func (m Map[V]) MarshalJSON() ([]byte, error) { return MarshalMap(m) }
 
 // ScanMap scans a nullable text or JSON into a map, using an empty map for NULL.
-func ScanMap(value any, m *Map) error {
+func ScanMap[V any](value any, m *Map[V]) error {
 	if value == nil {
-		*m = make(Map)
+		*m = make(Map[V])
 		return nil
 	}
 
@@ -40,7 +40,7 @@ func ScanMap(value any, m *Map) error {
 
 	// empty bytes is same as nil
 	if len(raw) == 0 {
-		*m = make(Map)
+		*m = make(Map[V])
 		return nil
 	}
 
@@ -52,29 +52,29 @@ func ScanMap(value any, m *Map) error {
 }
 
 // MapValue converts a map to NULL if it is empty.
-func MapValue(m Map) (driver.Value, error) {
+func MapValue[V any](m Map[V]) (driver.Value, error) {
 	if len(m) == 0 {
 		return nil, nil
 	}
 	return json.Marshal(m)
 }
 
 // MarshalMap marshals a map, returning null for an empty map.
-func MarshalMap(m Map) ([]byte, error) {
+func MarshalMap[V any](m Map[V]) ([]byte, error) {
 	if len(m) == 0 {
 		return json.Marshal(nil)
 	}
-	return json.Marshal(map[string]any(m))
+	return json.Marshal(map[string]V(m))
 }
 
-func UnmarshalMap(data []byte, m *Map) error {
-	err := json.Unmarshal(data, (*map[string]any)(m))
+func UnmarshalMap[V any](data []byte, m *Map[V]) error {
+	err := json.Unmarshal(data, (*map[string]V)(m))
 	if err != nil {
 		return err
 	}
 
 	if *m == nil {
-		*m = make(Map) // initialize empty map
+		*m = make(Map[V]) // initialize empty map
 	}
 	return nil
 }

map_test.go

@@ -15,13 +15,13 @@ func TestMap(t *testing.T) {
 
 	testMap := func() {
 		tcs := []struct {
-			value     null.Map
+			value     null.Map[string]
 			dbValue   driver.Value
 			marshaled []byte
 		}{
-			{null.Map{"foo": "bar"}, []byte(`{"foo":"bar"}`), []byte(`{"foo":"bar"}`)},
-			{null.Map{}, nil, []byte(`null`)},
-			{null.Map(nil), nil, []byte(`null`)},
+			{null.Map[string]{"foo": "bar"}, []byte(`{"foo":"bar"}`), []byte(`{"foo":"bar"}`)},
+			{null.Map[string]{}, nil, []byte(`null`)},
+			{null.Map[string](nil), nil, []byte(`null`)},
 		}
 
 		for _, tc := range tcs {
@@ -38,15 +38,15 @@ func TestMap(t *testing.T) {
 			rows, err := db.Query(`SELECT value FROM test;`)
 			assert.NoError(t, err)
 
-			scanned := null.Map{}
+			scanned := null.Map[string]{}
 			assert.True(t, rows.Next())
 			err = rows.Scan(&scanned)
 			assert.NoError(t, err)
 
 			// we never return a nil map even if that's what we wrote
 			expected := tc.value
 			if expected == nil {
-				expected = null.Map{}
+				expected = null.Map[string]{}
 			}
 
 			assert.Equal(t, expected, scanned, "scanned value mismatch for %v", tc.value)
@@ -55,7 +55,7 @@ func TestMap(t *testing.T) {
 			assert.NoError(t, err)
 			assert.Equal(t, tc.marshaled, marshaled, "marshaled mismatch for %v", tc.value)
 
-			unmarshaled := null.Map{}
+			unmarshaled := null.Map[string]{}
 			err = json.Unmarshal(marshaled, &unmarshaled)
 			assert.NoError(t, err)
 			assert.Equal(t, expected, unmarshaled, "unmarshaled mismatch for %v", tc.value)