README
¶
go-clone: Deep clone any Go data
Package clone provides functions to deep clone any Go data.
It also provides a wrapper to protect a pointer from any unexpected mutation.
Clone/Slowly can clone unexported fields of any struct. Use this feature wisely.
Install
Use go get to install this package.
go get github.com/huandu/go-clone
Usage
Clone and Slowly
If we want to clone any Go value, use Clone.
t := &T{...}
v := clone.Clone(t).(*T)
reflect.DeepEqual(t, v) // true
For the sake of performance, Clone doesn't deal with values containing pointer cycles.
If we need to clone such values, use Slowly instead.
type ListNode struct {
Data int
Next *ListNode
}
node1 := &ListNode{
Data: 1,
}
node2 := &ListNode{
Data: 2,
}
node3 := &ListNode{
Data: 3,
}
node1.Next = node2
node2.Next = node3
node3.Next = node1
// We must use `Slowly` to clone a circular linked list.
node := Slowly(node1).(*ListNode)
for i := 0; i < 10; i++ {
fmt.Println(node.Data)
node = node.Next
}
Mark struct type as scalar
Some struct types can be considered as scalar.
A well-known case is time.Time.
Although there is a pointer loc *time.Location inside time.Time, we always use time.Time by value in all methods.
When cloning time.Time, it should be OK to return a shadow copy.
Currently, following types are marked as scalar by default.
time.Timereflect.Value
If there is any type defined in built-in package should be considered as scalar, please open new issue to let me know. I will update the default.
If there is any custom type should be considered as scalar, call MarkAsScalar to mark it manually. See MarkAsScalar sample code for more details.
Wrap, Unwrap and Undo
Package clone provides Wrap/Unwrap functions to protect a pointer value from any unexpected mutation.
It's useful when we want to protect a variable which should be immutable by design,
e.g. global config, the value stored in context, the value sent to a chan, etc.
// Suppose we have a type T defined as following.
// type T struct {
// Foo int
// }
v := &T{
Foo: 123,
}
w := Wrap(v).(*T) // Wrap value to protect it.
// Use w freely. The type of w is the same as that of v.
// It's OK to modify w. The change will not affect v.
w.Foo = 456
fmt.Println(w.Foo) // 456
fmt.Println(v.Foo) // 123
// Once we need the original value stored in w, call `Unwrap`.
orig := Unwrap(w).(*T)
fmt.Println(orig == v) // true
fmt.Println(orig.Foo) // 123
// Or, we can simply undo any change made in w.
// Note that `Undo` is significantly slower than `Unwrap`, thus
// the latter is always preferred.
Undo(w)
fmt.Println(w.Foo) // 123
Performance
Here is the performance data running on my MacBook Pro.
MacBook Pro (15-inch, 2019)
Processor: 2.6 GHz Intel Core i7
go 1.13.7
goos: darwin
goarch: amd64
pkg: github.com/huandu/go-clone
BenchmarkSimpleClone-12 10254127 108 ns/op 32 B/op 1 allocs/op
BenchmarkComplexClone-12 667335 1831 ns/op 1472 B/op 22 allocs/op
BenchmarkUnwrap-12 13315618 91.2 ns/op 0 B/op 0 allocs/op
BenchmarkSimpleWrap-12 5119616 238 ns/op 48 B/op 1 allocs/op
BenchmarkComplexWrap-12 1000000 1158 ns/op 688 B/op 13 allocs/op
Similar packages
- Package encoding/gob: Gob encoder/decoder can be used to clone Go data. However, it's extremely slow.
- Package github.com/jinzhu/copier: Copy data by field name. It doesn't work with values containing pointer cycles.
- Package github.com/ulule/deepcopier: Another copier.
License
This package is licensed under MIT license. See LICENSE for details.
Documentation
¶
Overview ¶
Package clone provides functions to deep clone any Go data. It also provides a wrapper to protect a pointer from any unexpected mutation.
Index ¶
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Clone ¶
func Clone(v interface{}) interface{}
Clone recursively deep clone v to a new value. It assumes that there is no pointer cycle in v, e.g. v has a pointer points to v itself. If there is a pointer cycle, use Slowly instead.
In the most cases, Clone allocates new memory space for deep clone, instead of all scalar types and following special values.
- scalar types: all number-like types are copied by value.
- func: Copied by value as func is immutable at runtime.
- string: Copied by value as string is immutable by design.
- unsafe.Pointer: Copied by value as we don't know what's in it.
- chan: A new empty chan is cloned without any data inside.
Unlike many similar packages, Clone is able to clone unexported fields of any struct. Use this feature wisely.
func MarkAsScalar ¶ added in v1.1.2
MarkAsScalar marks t as a scalar type so that all clone methods will copy t by value. If t is not struct or pointer to struct, MarkAsScalar ignores t.
In the most cases, it's not necessary to call it explicitly. If a struct type contains scalar type fields only, the struct will be marked as scalar automatically.
Here is a list of types marked as scalar by default:
- time.Time
- reflect.Value
Example ¶
package main
import (
"fmt"
"os"
"reflect"
)
type ScalarType struct {
stderr *os.File
}
func main() {
MarkAsScalar(reflect.TypeOf(new(ScalarType)))
scalar := &ScalarType{
stderr: os.Stderr,
}
cloned := Clone(scalar).(*ScalarType)
// cloned is a shadow copy of scalar
// so that the pointer value should be the same.
fmt.Println(scalar.stderr == cloned.stderr)
}
Output: true
func Slowly ¶
func Slowly(v interface{}) interface{}
Slowly recursively deep clone v to a new value. It marks all cloned values internally, thus it can clone v with cycle pointer.
Slowly works exactly the same as Clone. See Clone doc for more details.
Example ¶
type ListNode struct {
Data int
Next *ListNode
}
node1 := &ListNode{
Data: 1,
}
node2 := &ListNode{
Data: 2,
}
node3 := &ListNode{
Data: 3,
}
node1.Next = node2
node2.Next = node3
node3.Next = node1
// We must use `Slowly` to clone a circular linked list.
node := Slowly(node1).(*ListNode)
for i := 0; i < 10; i++ {
fmt.Println(node.Data)
node = node.Next
}
Output: 1 2 3 1 2 3 1 2 3 1
func Undo ¶
func Undo(v interface{})
Undo discards any change made in wrapped value. If v is not a wrapped value, nothing happens.
func Unwrap ¶
func Unwrap(v interface{}) interface{}
Unwrap returns v's original value if v is a wrapped value. Otherwise, simply returns v itself.
func Wrap ¶
func Wrap(v interface{}) interface{}
Wrap creates a wrapper of v, which must be a pointer. If v is not a pointer, Wrap simply returns v and do nothing.
The wrapper is a deep clone of v's value. It holds a shadow copy to v internally.
t := &T{Foo: 123}
v := Wrap(t).(*T) // v is a clone of t.
reflect.DeepEqual(t, v) == true // v equals t.
v.Foo = 456 // v.Foo is changed, but t.Foo doesn't change.
orig := Unwrap(v) // Use `Unwrap` to discard wrapper and return original value, which is t.
orig.(*T) == t // orig and t is exactly the same.
Undo(v) // Use `Undo` to discard any change on v.
v.Foo == t.Foo // Now, the value of v and t are the same again.
Example ¶
// Suppose we have a type T defined as following.
// type T struct {
// Foo int
// }
v := &T{
Foo: 123,
}
w := Wrap(v).(*T) // Wrap value to protect it.
// Use w freely. The type of w is the same as that of v.
// It's OK to modify w. The change will not affect v.
w.Foo = 456
fmt.Println(w.Foo) // 456
fmt.Println(v.Foo) // 123
// Once we need the original value stored in w, call `Unwrap`.
orig := Unwrap(w).(*T)
fmt.Println(orig == v) // true
fmt.Println(orig.Foo) // 123
// Or, we can simply undo any change made in w.
// Note that `Undo` is significantly slower than `Unwrap`, thus
// the latter is always preferred.
Undo(w)
fmt.Println(w.Foo) // 123
Output: 456 123 true 123 123
Types ¶
This section is empty.
Source Files
Directories