Support unmarshaling values into result.Ok variants

Author: myusko

result/json.go

@@ -0,0 +1,18 @@
+package result
+
+import "encoding/json"
+
+// UnmarshalJSON implements the [json.Unmarshaler] interface.
+// Values will be unmarshaled as [Ok] variants.
+func (r *Result[T]) UnmarshalJSON(data []byte) error {
+	var value T
+
+	if err := json.Unmarshal(data, &value); err != nil {
+		return err
+	}
+
+	*r = Ok(value)
+	return nil
+}
+
+var _ json.Unmarshaler = &Result[struct{}]{}

result/json_test.go

@@ -0,0 +1,42 @@
+package result_test
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/BooleanCat/go-functional/internal/assert"
+	"github.com/BooleanCat/go-functional/result"
+	"testing"
+)
+
+func ExampleResult_UnmarshalJSON() {
+	var r result.Result[[]string]
+
+	_ = json.Unmarshal([]byte(`["Foo", "Bar"]`), &r)
+
+	value, _ := r.Value()
+
+	fmt.Println(value)
+
+	// Output:
+	// [Foo Bar]
+}
+
+func TestUnmarshalJSON(t *testing.T) {
+	var r result.Result[[]string]
+
+	err := json.Unmarshal([]byte(`["Foo", "Bar"]`), &r)
+	assert.Nil(t, err)
+
+	value, err := r.Value()
+	assert.Nil(t, err)
+
+	assert.SliceEqual(t, value, []string{"Foo", "Bar"})
+}
+
+func TestUnmarshalError(t *testing.T) {
+	var r result.Result[string]
+
+	err := json.Unmarshal([]byte("42"), &r)
+
+	assert.NotNil(t, err)
+}

result/result.go

@@ -1,6 +1,8 @@
 package result
 
-import "fmt"
+import (
+	"fmt"
+)
 
 // Result represents failure or success. The [Ok] variant represents success
 // and contains a value. The [Err] variant represent a failure and contains an