From 67d9ddd8b517896db8222e4ac398b6d7ccc36289 Mon Sep 17 00:00:00 2001
From: zed <zedsmail@163.com>
Date: Tue, 23 Apr 2024 17:58:07 +0800
Subject: [PATCH] feat: Copy to Nil pointer of struct

---
 copier.go      | 12 +++++++++++-
 copier_test.go | 18 ++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/copier.go b/copier.go
index 0cc6465..3550769 100644
--- a/copier.go
+++ b/copier.go
@@ -122,7 +122,7 @@ func copier(toValue interface{}, fromValue interface{}, opt Option) (err error)
 		isSlice    bool
 		amount     = 1
 		from       = indirect(reflect.ValueOf(fromValue))
-		to         = indirect(reflect.ValueOf(toValue))
+		to         = indirectAndFill(reflect.ValueOf(toValue))
 		converters = opt.converters()
 		mappings   = opt.fieldNameMapping()
 	)
@@ -544,6 +544,16 @@ func deepFields(reflectType reflect.Type) []reflect.StructField {
 	return res
 }
 
+func indirectAndFill(reflectValue reflect.Value) reflect.Value {
+	for reflectValue.Kind() == reflect.Ptr {
+		if reflectValue.IsNil() {
+			reflectValue.Set(reflect.New(reflectValue.Type().Elem()))
+		}
+		reflectValue = reflectValue.Elem()
+	}
+	return reflectValue
+}
+
 func indirect(reflectValue reflect.Value) reflect.Value {
 	for reflectValue.Kind() == reflect.Ptr {
 		reflectValue = reflectValue.Elem()
diff --git a/copier_test.go b/copier_test.go
index 4769eba..f510370 100644
--- a/copier_test.go
+++ b/copier_test.go
@@ -1762,3 +1762,21 @@ func TestNestedNilPointerStruct(t *testing.T) {
 		t.Errorf("to (%v) value should equal from (%v) value", to.Title, from.Title)
 	}
 }
+
+func TestCopyToNilPointerOfStruct(t *testing.T) {
+	type struct1 struct {
+		A int
+	}
+	type struct2 struct {
+		A int
+	}
+	s1 := struct1{A: 1}
+	var s2 *struct2
+	err := copier.Copy(&s2, s1)
+	if err != nil {
+		t.Error("should not error")
+	}
+	if s1.A != (*s2).A {
+		t.Error("should equal")
+	}
+}