add json support to Pointer (#180)

* add json support to Pointer
* update changelog
* coverage

CHANGELOG.md

@@ -5,7 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
-- No changes yet.
+### Added
+- Add `MarshalJSON` and `UnmarshalJSON` method to `atomic.Pointer[T]` type
+allowing users to use pointer with json.
 
 ## [1.11.0] - 2023-05-02
 ### Fixed

pointer_go118.go

@@ -23,9 +23,27 @@
 
 package atomic
 
-import "fmt"
+import (
+	"encoding/json"
+	"fmt"
+)
 
 // String returns a human readable representation of a Pointer's underlying value.
 func (p *Pointer[T]) String() string {
 	return fmt.Sprint(p.Load())
 }
+
+// MarshalJSON encodes the wrapped pointer into JSON.
+func (p *Pointer[T]) MarshalJSON() ([]byte, error) {
+	return json.Marshal(p.Load())
+}
+
+// UnmarshalJSON decodes JSON into the wrapped pointer.
+func (p *Pointer[T]) UnmarshalJSON(b []byte) error {
+	var v T
+	if err := json.Unmarshal(b, &v); err != nil {
+		return err
+	}
+	p.Store(&v)
+	return nil
+}

pointer_test.go

@@ -24,14 +24,17 @@
 package atomic
 
 import (
+	"encoding/json"
 	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
 )
 
 func TestPointer(t *testing.T) {
-	type foo struct{ v int }
+	type foo struct {
+		V int `json:"v"`
+	}
 
 	i := foo{42}
 	j := foo{0}
@@ -94,6 +97,28 @@ func TestPointer(t *testing.T) {
 				atom := tt.newAtomic()
 				require.Equal(t, fmt.Sprint(tt.initial), atom.String(), "String did not return the correct value.")
 			})
+
+			t.Run("MarshalJSON", func(t *testing.T) {
+				atom := tt.newAtomic()
+				marshaledPointer, err := json.Marshal(atom)
+				require.NoError(t, err)
+				marshaledRaw, err := json.Marshal(tt.initial)
+				require.NoError(t, err)
+				require.Equal(t, marshaledRaw, marshaledPointer, "MarshalJSON did not return the correct value.")
+			})
 		})
 	}
+
+	t.Run("UnmarshalJSON", func(t *testing.T) {
+		var p Pointer[foo]
+
+		require.NoError(t, json.Unmarshal([]byte(`{"v":1024}`), &p))
+		require.Equal(t, 1024, p.Load().V, "UnmarshalJSON should have expected result")
+	})
+
+	t.Run("UnmarshalJSON error", func(t *testing.T) {
+		var p Pointer[foo]
+
+		require.Error(t, json.Unmarshal([]byte(`{"v":true}`), &p), "json.Unmarshal should return an error")
+	})
 }