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clone.go
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clone.go
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package genh
import (
"reflect"
"sync"
)
var cloneCache struct {
m map[reflect.Type]int
sync.RWMutex
}
func hasCloner(t reflect.Type) int {
cloneCache.RLock()
v, ok := cloneCache.m[t]
cloneCache.RUnlock()
if ok {
return v
}
cloneCache.Lock()
defer cloneCache.Unlock()
if cloneCache.m == nil {
cloneCache.m = make(map[reflect.Type]int)
}
if hasClone(t) {
v = 1
} else if hasClone(reflect.PtrTo(t)) {
v = 2
}
cloneCache.m[t] = v
return v
}
func hasClone(t reflect.Type) bool {
m, ok := t.MethodByName("Clone")
if !ok {
return false
}
if m.Type.NumOut() != 1 {
return false
}
if ot := m.Type.Out(0); ot != m.Type.In(0) {
return false
}
return true
}
type Cloner[T any] interface {
Clone() T
}
func Clone[T any](v T, keepPrivateFields bool) (cp T) {
if v, ok := any(v).(Cloner[T]); ok {
return v.Clone()
}
src, dst := reflect.ValueOf(v), reflect.ValueOf(&cp).Elem()
ReflectClone(dst, src, keepPrivateFields)
return
}
func ReflectClone(dst, src reflect.Value, keepPrivateFields bool) {
if !src.IsValid() || src.IsZero() {
return
}
if src.Kind() == reflect.Interface {
src = src.Elem()
}
styp := src.Type()
if cloneVal(dst, src) {
return
}
switch styp.Kind() {
case reflect.Slice:
if src.IsNil() {
return
}
dst.Set(reflect.MakeSlice(styp, src.Len(), src.Cap()))
fallthrough
case reflect.Array:
for i := 0; i < src.Len(); i++ {
dst, src := dst.Index(i), src.Index(i)
if dst.Kind() != reflect.Interface {
ReflectClone(dst, src, keepPrivateFields)
continue
}
if src.Kind() == reflect.Interface {
src = src.Elem()
}
ndst := reflect.New(src.Type()).Elem()
ReflectClone(ndst, src, keepPrivateFields)
dst.Set(ndst)
}
case reflect.Map:
if src.IsNil() {
return
}
dst.Set(reflect.MakeMapWithSize(styp, src.Len()))
for it := src.MapRange(); it.Next(); {
mk, mv := maybeCopy(it.Key(), keepPrivateFields), maybeCopy(it.Value(), keepPrivateFields)
dst.SetMapIndex(mk, mv)
}
case reflect.Struct:
if keepPrivateFields {
dst.Set(src) // copy private fields
} else {
dst.Set(reflect.New(styp).Elem())
}
for i := 0; i < styp.NumField(); i++ {
if f := dst.Field(i); f.CanSet() {
ReflectClone(dst.Field(i), src.Field(i), keepPrivateFields)
}
}
case reflect.Ptr:
if src.IsNil() {
return
}
ndst := reflect.New(styp.Elem())
ReflectClone(ndst.Elem(), src.Elem(), keepPrivateFields)
dst.Set(ndst)
default:
dst.Set(src)
}
}
func maybeCopy(src reflect.Value, copyPrivate bool) reflect.Value {
switch src.Kind() {
case reflect.Ptr, reflect.Array, reflect.Slice, reflect.Map:
nv := reflect.New(src.Type()).Elem()
ReflectClone(nv, src, copyPrivate)
return nv
case reflect.Interface:
return maybeCopy(src.Elem(), copyPrivate)
default:
return src
}
}
func cloneVal(dst, src reflect.Value) bool {
var m reflect.Value
switch hasCloner(src.Type()) {
case 1:
m = src.MethodByName("Clone")
case 2:
if src.CanAddr() {
m = src.Addr().MethodByName("Clone")
}
default:
return false
}
v := m.Call(nil)[0]
if v.Kind() == reflect.Interface {
v = v.Elem()
}
if v.Kind() == reflect.Ptr && dst.Kind() != reflect.Ptr {
v = v.Elem()
}
dst.Set(v)
return true
}