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package clone
import (
"reflect"
"unsafe"
)
const sizeOfPointers = unsafe.Sizeof((interface{})(0)) / unsafe.Sizeof(uintptr(0))
// interfaceData is the underlying data of an interface.
// As the reflect.Value's interfaceData method is deprecated,
// it may be broken in any Go release.
// It's better to create a custom to hold the data.
//
// The type of interfaceData fields must be poniters.
// It's a way to cheat Go compile to generate calls to write barrier
// when copying interfaces.
type interfaceData struct {
_ [sizeOfPointers]unsafe.Pointer
}
var reflectValuePtrOffset uintptr
func init() {
t := reflect.TypeOf(reflect.Value{})
found := false
fields := t.NumField()
for i := 0; i < fields; i++ {
field := t.Field(i)
if field.Type.Kind() == reflect.UnsafePointer {
found = true
reflectValuePtrOffset = field.Offset
break
}
}
if !found {
panic("go-clone: fail to find internal ptr field in reflect.Value")
}
}
// parseReflectValue returns the underlying interface data in a reflect value.
// It assumes that v is an interface value.
func parseReflectValue(v reflect.Value) interfaceData {
pv := (unsafe.Pointer)(uintptr(unsafe.Pointer(&v)) + reflectValuePtrOffset)
ptr := *(*unsafe.Pointer)(pv)
return *(*interfaceData)(ptr)
}
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