fix: preserve initial values in pointer-to-struct slices

env.go

@@ -461,13 +461,14 @@ func doParseSlice(ref reflect.Value, processField processFieldFn, opts Options)
 		}
 
 		sliceType := ref.Type()
+		initial := ref
 		var initialized int
 		if reflect.Pointer == ref.Kind() {
 			sliceType = sliceType.Elem()
-			// Due to the rest of code the pre-initialized slice has no chance for this situation
-			initialized = 0
-		} else {
-			initialized = ref.Len()
+			initial = ref.Elem()
+		}
+		if initial.IsValid() {
+			initialized = initial.Len()
 		}
 
 		var capacity int
@@ -478,7 +479,7 @@ func doParseSlice(ref reflect.Value, processField processFieldFn, opts Options)
 		for i := 0; i < capacity; i++ {
 			item := result.Index(i)
 			if i < initialized {
-				item.Set(ref.Index(i))
+				item.Set(initial.Index(i))
 			}
 			if err := doParse(item, processField, optionsWithSliceEnvPrefix(opts, i)); err != nil {
 				return err

slice_pointer_defaults_test.go

@@ -0,0 +1,17 @@
+package env
+
+import "testing"
+
+func TestSlicePointerPreservesInitialValues(t *testing.T) {
+	type item struct {
+		Name string `env:"NAME"`
+		Port int    `env:"PORT"`
+	}
+	items := []item{{Name: "first", Port: 8080}, {Name: "second", Port: 9090}}
+	cfg := struct {
+		Items *[]item `envPrefix:"ITEMS_"`
+	}{Items: &items}
+	err := ParseWithOptions(&cfg, Options{Environment: map[string]string{"ITEMS_0_NAME": "updated"}})
+	isNoErr(t, err)
+	isEqual(t, []item{{Name: "updated", Port: 8080}, {Name: "second", Port: 9090}}, *cfg.Items)
+}