deepcopy

Usages

eventdeep.New, eventdeep.MakeClone and eventdeep.DeepCopy are main entries.

By default, DeepCopy() will copy and merge source into destination object. That means, a map or a slice will be merged deeply, same to a struct.

New(opts...) gives a most even scalable interface than DeepCopy, it returns a new DeepCopier different to DefaultCopyController and you can make call to DeepCopier.DeepCopy(old, new, opts...).

In copy-n-merge mode, copying [2, 3] to [3, 7] will get [3, 7, 2].

Getting Started

Here is a basic sample code:

func TestExample1(t *testing.T) {
  timeZone, _ := time.LoadLocation("America/Phoenix")
  tm := time.Date(1999, 3, 13, 5, 57, 11, 1901, timeZone)
  src := eventdeep.Employee2{
    Base: eventdeep.Base{
      Name:      "Bob",
      Birthday:  &tm,
      Age:       24,
      EmployeID: 7,
    },
    Avatar: "https://tse4-mm.cn.bing.net/th/id/OIP-C.SAy__OKoxrIqrXWAb7Tj1wHaEC?pid=ImgDet&rs=1",
    Image:  []byte{95, 27, 43, 66, 0, 21, 210},
    Attr:   &eventdeep.Attr{Attrs: []string{"hello", "world"}},
    Valid:  true,
  }
  var dst eventdeep.User
 
  // direct way but no error report: eventdeep.DeepCopy(src, &dst)
  c := eventdeep.New()
  if err := c.CopyTo(src, &dst); err != nil {
    t.Fatal(err)
  }
  if !reflect.DeepEqual(dst, eventdeep.User{
    Name:      "Bob",
    Birthday:  &tm,
    Age:       24,
    EmployeID: 7,
    Avatar:    "https://tse4-mm.cn.bing.net/th/id/OIP-C.SAy__OKoxrIqrXWAb7Tj1wHaEC?pid=ImgDet&rs=1",
    Image:     []byte{95, 27, 43, 66, 0, 21, 210},
    Attr:      &eventdeep.Attr{Attrs: []string{"hello", "world"}},
    Valid:     true,
  }) {
    t.Fatalf("bad, got %v", dst)
  }
}

Customizing The Field Extractor

For the unconventional deep copy, we can copy field to field via a source extractor.

You need a target struct at first.

func TestStructWithSourceExtractor(t *testing.T) {
  c := context.WithValue(context.TODO(), "Data", map[string]typ.Any{
    "A": 12,
  })
 
  tgt := struct {
    A int
  }{}
 
  evendeep.DeepCopy(c, &tgt, evendeep.WithSourceValueExtractor(func(name string) typ.Any {
    if m, ok := c.Value("Data").(map[string]typ.Any); ok {
      return m[name]
    }
    return nil
  }))
 
  if tgt.A != 12 {
    t.FailNow()
  }
}

Customizing The Target Setter

As a contrary, you might specify a setter to handle the setting action on copying struct and/or map.

func TestStructWithTargetSetter(t *testing.T) {
  type srcS struct {
    A int
    B bool
    C string
  }
 
  src := &srcS{
    A: 5,
    B: true,
    C: "helloString",
  }
  tgt := map[string]typ.Any{
    "Z": "str",
  }
 
  err := evendeep.New().CopyTo(src, &tgt,
    evendeep.WithTargetValueSetter(func(value *reflect.Value, sourceNames ...string) (err error) {
      if value != nil {
        name := "Mo" + strings.Join(sourceNames, ".")
        tgt[name] = value.Interface()
      }
      return // ErrShouldFallback to call the evendeep standard processing
    }),
  )
 
  if err != nil || tgt["MoA"] != 5 || tgt["MoB"] != true || tgt["MoC"] != "helloString" || tgt["Z"] != "str" {
    t.Errorf("err: %v, tgt: %v", err, tgt)
    t.FailNow()
  }
}

NOTE that the feature is only fit for copying on/between struct and/or map.

If you really wanna customize the setter for primitives or others, concern to implement a ValueCopier or ValueConverter.

`ByOrdinal` or `ByName`

evendeep enumerates fields in struct/map/slice with two strategies: ByOrdinal and ByName.

Default ByOrdinal assumes the copier loops all source fields and copy them to the corresponding destination with the ordinal order.
ByName strategy assumes the copier loops all target fields, and try copying value from the coressponding source field by its name.

When a name conversion rule is defined in a struct field tag, the copier will look for the name and copy value to, even if it's in ByOrdinal mode.

Customizing A Converter

The customized Type/Value Converter can be applied on transforming the data from source. For more information take a look ValueConverter and ValueCopier. Its take effects on checking the value type of target or source, or both of them.

type MyType struct {
  I int
}
 
type MyTypeToStringConverter struct{}
 
// Uncomment this line if you wanna implment a ValueCopier implementation too:
// func (c *MyTypeToStringConverter) CopyTo(ctx *eventdeep.ValueConverterContext, source, target reflect.Value) (err error) { return }
 
func (c *MyTypeToStringConverter) Transform(ctx *eventdeep.ValueConverterContext, source reflect.Value, targetType reflect.Type) (target reflect.Value, err error) {
  if source.IsValid() && targetType.Kind() == reflect.String {
    var str string
    if str, err = eventdeep.FallbackToBuiltinStringMarshalling(source); err == nil {
      target = reflect.ValueOf(str)
    }
  }
  return
}
 
func (c *MyTypeToStringConverter) Match(params *eventdeep.Params, source, target reflect.Type) (ctx *eventdeep.ValueConverterContext, yes bool) {
  sn, sp := source.Name(), source.PkgPath()
  sk, tk := source.Kind(), target.Kind()
  if yes = sk == reflect.Struct && tk == reflect.String &&
    sn == "MyType" && sp == "github.com/hedzr/eventdeep_test"; yes {
    ctx = &eventdeep.ValueConverterContext{Params: params}
  }
  return
}
 
func TestExample2(t *testing.T) {
  var myData = MyType{I: 9}
  var dst string
  eventdeep.DeepCopy(myData, &dst, eventdeep.WithValueConverters(&MyTypeToStringConverter{}))
  if dst != `{
  "I": 9
}` {
    t.Fatalf("bad, got %v", dst)
  }
}

Instead of WithValueConverters / WithValueCopiers for each times invoking New(), you might register yours once by calling RegisterDefaultConverters / RegisterDefaultCopiers into global registry.

  // a stub call for coverage
  eventdeep.RegisterDefaultCopiers()
 
  var dst1 string
  eventdeep.RegisterDefaultConverters(&MyTypeToStringConverter{})
  eventdeep.DeepCopy(myData, &dst1)
  if dst1 != `{
  "I": 9
}` {
    t.Fatalf("bad, got %v", dst)
  }

Zero Target Fields If Equals To Source

When we compare two Struct, the target one can be clear to zero except a field value is not equal to source field. This feature can be used for your ORM codes: someone loads a record as a golang struct variable, and make some changes, and invoking eventdeep.DeepCopy(originRec, &newRecord, eventdeep.WithORMDiffOpt), the changes will be kept in newRecord and the others unchanged fields be cleanup at last.

The codes are:

func TestExample3(t *testing.T) {
  timeZone, _ := time.LoadLocation("America/Phoenix")
  tm := time.Date(1999, 3, 13, 5, 57, 11, 1901, timeZone)
  var originRec = eventdeep.User{ ... }
  var newRecord eventdeep.User
  var t0 = time.Unix(0, 0)
  var expectRec = eventdeep.User{Name: "Barbara", Birthday: &t0, Attr: &eventdeep.Attr{}}
 
  eventdeep.DeepCopy(originRec, &newRecord)
  t.Logf("newRecord: %v", newRecord)
 
  newRecord.Name = "Barbara"
  eventdeep.DeepCopy(originRec, &newRecord, eventdeep.WithORMDiffOpt)
  ...
  if !reflect.DeepEqual(newRecord, expectRec) {
    t.Fatalf("bad, got %v | %v", newRecord, newRecord.Birthday.Nanosecond())
  }
}

Keep The Target Value If Source Is Empty

Sometimes we would look for a do-not-modify copier, it'll keep the value of target fields while the corresponding source field is empty (zero or nil). Use eventdeep.WithOmitEmptyOpt in the case.

func TestExample4(t *testing.T) {
  timeZone, _ := time.LoadLocation("America/Phoenix")
  tm := time.Date(1999, 3, 13, 5, 57, 11, 1901, timeZone)
  var originRec = eventdeep.User{
    Name:      "Bob",
    Birthday:  &tm,
    Age:       24,
    EmployeID: 7,
    Avatar:    "https://tse4-mm.cn.bing.net/th/id/OIP-C.SAy__OKoxrIqrXWAb7Tj1wHaEC?pid=ImgDet&rs=1",
    Image:     []byte{95, 27, 43, 66, 0, 21, 210},
    Attr:      &eventdeep.Attr{Attrs: []string{"hello", "world"}},
    Valid:     true,
  }
  var dstRecord eventdeep.User
  var t0 = time.Unix(0, 0)
  var emptyRecord = eventdeep.User{Name: "Barbara", Birthday: &t0}
  var expectRecord = eventdeep.User{Name: "Barbara", Birthday: &t0,
    Image: []byte{95, 27, 43, 66, 0, 21, 210},
    Attr:  &eventdeep.Attr{Attrs: []string{"hello", "world"}},
    Valid: true,
  }
 
  // prepare a hard copy at first
  eventdeep.DeepCopy(originRec, &dstRecord)
  t.Logf("dstRecord: %v", dstRecord)
 
  // now update dstRecord with the non-empty fields.
  eventdeep.DeepCopy(emptyRecord, &dstRecord, eventdeep.WithOmitEmptyOpt)
  t.Logf("dstRecord: %v", dstRecord)
  if !reflect.DeepEqual(dstRecord, expectRecord) {
    t.Fatalf("bad, got %v\nexpect: %v", dstRecord, expectRecord)
  }
}

String Marshalling

While copying struct, map, slice, or other source to target string, the builtin toStringConverter will be launched. And the default logic includes marshaling the structural source to string, typically json.Marshal.

This marshaller can be customized: RegisterStringMarshaller and WithStringMarshaller enable it:

eventdeep.RegisterStringMarshaller(yaml.Marshal)
eventdeep.RegisterStringMarshaller(json.Marshal)

The default marshaler is a wraper to json.MarshalIndent.

Specify CopyMergeStrategy via struct Tag

Sample struct is (use copy as key):

type AFT struct {
  flags     flags.Flags `copy:",cleareq"`
  converter *ValueConverter
  wouldbe   int `copy:",must,keepneq,omitzero,mapmerge"`
  ignored1 int `copy:"-"`
  ignored2 int `copy:",-"`
}

Name conversions

copy tag has form: nameConversion[,strategies...]. nameConversion gives a target field Name to define a name conversion strategy, or - to ignore the field.

nameConversion has form:

-: field is ignored
targetName
->targetName
sourceName->targetName

Spaces besides of -> are allowed.

Copier will check target field tag at first, and following by a source field tag checking.

You may specify converting rule at either target or source side, Copier assume the target one is prior.

NOTE: nameConversion is fully functional only for cms.ByName mode. It get partial work in cms.ByOrdinal mode ( default mode).

TODO: In cms.ByOrdinal (*) mode, a name converter can be applied in copying field to field.

Sample codes

The test gives a sample to show you how the name-conversion and member function work together:

func TestStructWithNameConversions(t *testing.T) {
  type srcS struct {
    A int    `copy:"A1"`
    B bool   `copy:"B1,std"`
    C string `copy:"C1,"`
  }
 
  type dstS struct {
    A1 int
    B1 bool
    C1 string
  }
 
  src := &srcS{A: 6, B: true, C: "hello"}
  var tgt = dstS{A1: 1}
 
  // use ByName strategy,
  err := evendeep.New().CopyTo(src, &tgt, evendeep.WithByNameStrategyOpt)
 
  if tgt.A1 != 6 || !tgt.B1 || tgt.C1 != "hello" || err != nil {
    t.Fatalf("BAD COPY, tgt: %+v", tgt)
  }
}

Strategy Names

The available tag names are (Almost newest, see its in flags/cms/copymergestrategy.go):

Tag name	Flags	Detail
`-`	`cms.Ignore`	field will be ignored
`std` (*)	`cms.Default`	reserved
`must`	`cms.Must`	reserved
`cleareq`	`cms.ClearIfEqual`	set zero if target equal to source
`keepneq`	`cms.KeepIfNotEq`	don't copy source if target not equal to source
`clearinvalid`	`cms.ClearIfInvalid`	if target field is invalid, set to zero value
`noomit` (*)	`cms.NoOmit`
`omitempty`	`cms.OmitIfEmpty`	if source field is empty, keep destination value
`omitnil`	`cms.OmitIfNil`
`omitzero`	`cms.OmitIfZero`
`noomittarget` (*)	`cms.NoOmitTarget`
`omitemptytarget`	`cms.OmitIfTargetEmpty`	if target field is empty, don't copy from source
`omitniltarget`	`cms.OmitIfTargetNil`
`omitzerotarget`	`cms.OmitIfTargetZero`
`slicecopy`	`cms.SliceCopy`	copy elem by subscription
`slicecopyappend`	`cms.SliceCopyAppend`	and append more
`slicemerge`	`cms.SliceMerge`	merge with order-insensitive
`mapcopy`	`cms.MapCopy`	copy elem by key
`mapmerge`	`cms.MapMerge`	merge map deeply
...

*: the flag is on by default.

Notes About `DeepCopy()`

Many settings are accumulated in multiple calling on DeepCopy(), such as converters, ignoreNames, and so on. The underlying object is DefaultCopyController.

To get a fresh clean copier, New() or NewFlatDeepCopier() are the choices. BTW, sometimes evendeep.ResetDefaultCopyController() might be helpful.

The only exception is copy-n-merge strategies. There flags are saved and restored on each calling on DeepCopy().

Notes About Global Settings

Some settings are global and available to both of DeepCopy() and New().CopyTo(), such as:

WithStringMarshaller or RegisterDefaultStringMarshaller()
RegisterDefaultConverters
RegisterDefaultCopiers

And so on.

Usages

deepcopy

eventdeep.New, eventdeep.MakeClone and eventdeep.DeepCopy are main entries.

By default, DeepCopy() will copy and merge source into destination object. That means, a map or a slice will be merged deeply, same to a struct.

In copy-n-merge mode, copying [2, 3] to [3, 7] will get [3, 7, 2].

Getting Started

Here is a basic sample code:

func TestExample1(t *testing.T) {
  timeZone, _ := time.LoadLocation("America/Phoenix")
  tm := time.Date(1999, 3, 13, 5, 57, 11, 1901, timeZone)
  src := eventdeep.Employee2{
    Base: eventdeep.Base{
      Name:      "Bob",
      Birthday:  &tm,
      Age:       24,
      EmployeID: 7,
    },
    Avatar: "https://tse4-mm.cn.bing.net/th/id/OIP-C.SAy__OKoxrIqrXWAb7Tj1wHaEC?pid=ImgDet&rs=1",
    Image:  []byte{95, 27, 43, 66, 0, 21, 210},
    Attr:   &eventdeep.Attr{Attrs: []string{"hello", "world"}},
    Valid:  true,
  }
  var dst eventdeep.User
 
  // direct way but no error report: eventdeep.DeepCopy(src, &dst)
  c := eventdeep.New()
  if err := c.CopyTo(src, &dst); err != nil {
    t.Fatal(err)
  }
  if !reflect.DeepEqual(dst, eventdeep.User{
    Name:      "Bob",
    Birthday:  &tm,
    Age:       24,
    EmployeID: 7,
    Avatar:    "https://tse4-mm.cn.bing.net/th/id/OIP-C.SAy__OKoxrIqrXWAb7Tj1wHaEC?pid=ImgDet&rs=1",
    Image:     []byte{95, 27, 43, 66, 0, 21, 210},
    Attr:      &eventdeep.Attr{Attrs: []string{"hello", "world"}},
    Valid:     true,
  }) {
    t.Fatalf("bad, got %v", dst)
  }
}

Customizing The Field Extractor

For the unconventional deep copy, we can copy field to field via a source extractor.

You need a target struct at first.

func TestStructWithSourceExtractor(t *testing.T) {
  c := context.WithValue(context.TODO(), "Data", map[string]typ.Any{
    "A": 12,
  })
 
  tgt := struct {
    A int
  }{}
 
  evendeep.DeepCopy(c, &tgt, evendeep.WithSourceValueExtractor(func(name string) typ.Any {
    if m, ok := c.Value("Data").(map[string]typ.Any); ok {
      return m[name]
    }
    return nil
  }))
 
  if tgt.A != 12 {
    t.FailNow()
  }
}

Customizing The Target Setter

As a contrary, you might specify a setter to handle the setting action on copying struct and/or map.

func TestStructWithTargetSetter(t *testing.T) {
  type srcS struct {
    A int
    B bool
    C string
  }
 
  src := &srcS{
    A: 5,
    B: true,
    C: "helloString",
  }
  tgt := map[string]typ.Any{
    "Z": "str",
  }
 
  err := evendeep.New().CopyTo(src, &tgt,
    evendeep.WithTargetValueSetter(func(value *reflect.Value, sourceNames ...string) (err error) {
      if value != nil {
        name := "Mo" + strings.Join(sourceNames, ".")
        tgt[name] = value.Interface()
      }
      return // ErrShouldFallback to call the evendeep standard processing
    }),
  )
 
  if err != nil || tgt["MoA"] != 5 || tgt["MoB"] != true || tgt["MoC"] != "helloString" || tgt["Z"] != "str" {
    t.Errorf("err: %v, tgt: %v", err, tgt)
    t.FailNow()
  }
}

NOTE that the feature is only fit for copying on/between struct and/or map.

If you really wanna customize the setter for primitives or others, concern to implement a ValueCopier or ValueConverter.

`ByOrdinal` or `ByName`

evendeep enumerates fields in struct/map/slice with two strategies: ByOrdinal and ByName.

Default ByOrdinal assumes the copier loops all source fields and copy them to the corresponding destination with the ordinal order.
ByName strategy assumes the copier loops all target fields, and try copying value from the coressponding source field by its name.

When a name conversion rule is defined in a struct field tag, the copier will look for the name and copy value to, even if it's in ByOrdinal mode.

Customizing A Converter

type MyType struct {
  I int
}
 
type MyTypeToStringConverter struct{}
 
// Uncomment this line if you wanna implment a ValueCopier implementation too:
// func (c *MyTypeToStringConverter) CopyTo(ctx *eventdeep.ValueConverterContext, source, target reflect.Value) (err error) { return }
 
func (c *MyTypeToStringConverter) Transform(ctx *eventdeep.ValueConverterContext, source reflect.Value, targetType reflect.Type) (target reflect.Value, err error) {
  if source.IsValid() && targetType.Kind() == reflect.String {
    var str string
    if str, err = eventdeep.FallbackToBuiltinStringMarshalling(source); err == nil {
      target = reflect.ValueOf(str)
    }
  }
  return
}
 
func (c *MyTypeToStringConverter) Match(params *eventdeep.Params, source, target reflect.Type) (ctx *eventdeep.ValueConverterContext, yes bool) {
  sn, sp := source.Name(), source.PkgPath()
  sk, tk := source.Kind(), target.Kind()
  if yes = sk == reflect.Struct && tk == reflect.String &&
    sn == "MyType" && sp == "github.com/hedzr/eventdeep_test"; yes {
    ctx = &eventdeep.ValueConverterContext{Params: params}
  }
  return
}
 
func TestExample2(t *testing.T) {
  var myData = MyType{I: 9}
  var dst string
  eventdeep.DeepCopy(myData, &dst, eventdeep.WithValueConverters(&MyTypeToStringConverter{}))
  if dst != `{
  "I": 9
}` {
    t.Fatalf("bad, got %v", dst)
  }
}

  // a stub call for coverage
  eventdeep.RegisterDefaultCopiers()
 
  var dst1 string
  eventdeep.RegisterDefaultConverters(&MyTypeToStringConverter{})
  eventdeep.DeepCopy(myData, &dst1)
  if dst1 != `{
  "I": 9
}` {
    t.Fatalf("bad, got %v", dst)
  }

Zero Target Fields If Equals To Source

The codes are:

func TestExample3(t *testing.T) {
  timeZone, _ := time.LoadLocation("America/Phoenix")
  tm := time.Date(1999, 3, 13, 5, 57, 11, 1901, timeZone)
  var originRec = eventdeep.User{ ... }
  var newRecord eventdeep.User
  var t0 = time.Unix(0, 0)
  var expectRec = eventdeep.User{Name: "Barbara", Birthday: &t0, Attr: &eventdeep.Attr{}}
 
  eventdeep.DeepCopy(originRec, &newRecord)
  t.Logf("newRecord: %v", newRecord)
 
  newRecord.Name = "Barbara"
  eventdeep.DeepCopy(originRec, &newRecord, eventdeep.WithORMDiffOpt)
  ...
  if !reflect.DeepEqual(newRecord, expectRec) {
    t.Fatalf("bad, got %v | %v", newRecord, newRecord.Birthday.Nanosecond())
  }
}

Keep The Target Value If Source Is Empty

Sometimes we would look for a do-not-modify copier, it'll keep the value of target fields while the corresponding source field is empty (zero or nil). Use eventdeep.WithOmitEmptyOpt in the case.

func TestExample4(t *testing.T) {
  timeZone, _ := time.LoadLocation("America/Phoenix")
  tm := time.Date(1999, 3, 13, 5, 57, 11, 1901, timeZone)
  var originRec = eventdeep.User{
    Name:      "Bob",
    Birthday:  &tm,
    Age:       24,
    EmployeID: 7,
    Avatar:    "https://tse4-mm.cn.bing.net/th/id/OIP-C.SAy__OKoxrIqrXWAb7Tj1wHaEC?pid=ImgDet&rs=1",
    Image:     []byte{95, 27, 43, 66, 0, 21, 210},
    Attr:      &eventdeep.Attr{Attrs: []string{"hello", "world"}},
    Valid:     true,
  }
  var dstRecord eventdeep.User
  var t0 = time.Unix(0, 0)
  var emptyRecord = eventdeep.User{Name: "Barbara", Birthday: &t0}
  var expectRecord = eventdeep.User{Name: "Barbara", Birthday: &t0,
    Image: []byte{95, 27, 43, 66, 0, 21, 210},
    Attr:  &eventdeep.Attr{Attrs: []string{"hello", "world"}},
    Valid: true,
  }
 
  // prepare a hard copy at first
  eventdeep.DeepCopy(originRec, &dstRecord)
  t.Logf("dstRecord: %v", dstRecord)
 
  // now update dstRecord with the non-empty fields.
  eventdeep.DeepCopy(emptyRecord, &dstRecord, eventdeep.WithOmitEmptyOpt)
  t.Logf("dstRecord: %v", dstRecord)
  if !reflect.DeepEqual(dstRecord, expectRecord) {
    t.Fatalf("bad, got %v\nexpect: %v", dstRecord, expectRecord)
  }
}

String Marshalling

This marshaller can be customized: RegisterStringMarshaller and WithStringMarshaller enable it:

eventdeep.RegisterStringMarshaller(yaml.Marshal)
eventdeep.RegisterStringMarshaller(json.Marshal)

The default marshaler is a wraper to json.MarshalIndent.

Specify CopyMergeStrategy via struct Tag

Sample struct is (use copy as key):

type AFT struct {
  flags     flags.Flags `copy:",cleareq"`
  converter *ValueConverter
  wouldbe   int `copy:",must,keepneq,omitzero,mapmerge"`
  ignored1 int `copy:"-"`
  ignored2 int `copy:",-"`
}

Name conversions

copy tag has form: nameConversion[,strategies...]. nameConversion gives a target field Name to define a name conversion strategy, or - to ignore the field.

nameConversion has form:

-: field is ignored
targetName
->targetName
sourceName->targetName

Spaces besides of -> are allowed.

Copier will check target field tag at first, and following by a source field tag checking.

You may specify converting rule at either target or source side, Copier assume the target one is prior.

NOTE: nameConversion is fully functional only for cms.ByName mode. It get partial work in cms.ByOrdinal mode ( default mode).

TODO: In cms.ByOrdinal (*) mode, a name converter can be applied in copying field to field.

Sample codes

The test gives a sample to show you how the name-conversion and member function work together:

func TestStructWithNameConversions(t *testing.T) {
  type srcS struct {
    A int    `copy:"A1"`
    B bool   `copy:"B1,std"`
    C string `copy:"C1,"`
  }
 
  type dstS struct {
    A1 int
    B1 bool
    C1 string
  }
 
  src := &srcS{A: 6, B: true, C: "hello"}
  var tgt = dstS{A1: 1}
 
  // use ByName strategy,
  err := evendeep.New().CopyTo(src, &tgt, evendeep.WithByNameStrategyOpt)
 
  if tgt.A1 != 6 || !tgt.B1 || tgt.C1 != "hello" || err != nil {
    t.Fatalf("BAD COPY, tgt: %+v", tgt)
  }
}

Strategy Names

The available tag names are (Almost newest, see its in flags/cms/copymergestrategy.go):

Tag name	Flags	Detail
`-`	`cms.Ignore`	field will be ignored
`std` (*)	`cms.Default`	reserved
`must`	`cms.Must`	reserved
`cleareq`	`cms.ClearIfEqual`	set zero if target equal to source
`keepneq`	`cms.KeepIfNotEq`	don't copy source if target not equal to source
`clearinvalid`	`cms.ClearIfInvalid`	if target field is invalid, set to zero value
`noomit` (*)	`cms.NoOmit`
`omitempty`	`cms.OmitIfEmpty`	if source field is empty, keep destination value
`omitnil`	`cms.OmitIfNil`
`omitzero`	`cms.OmitIfZero`
`noomittarget` (*)	`cms.NoOmitTarget`
`omitemptytarget`	`cms.OmitIfTargetEmpty`	if target field is empty, don't copy from source
`omitniltarget`	`cms.OmitIfTargetNil`
`omitzerotarget`	`cms.OmitIfTargetZero`
`slicecopy`	`cms.SliceCopy`	copy elem by subscription
`slicecopyappend`	`cms.SliceCopyAppend`	and append more
`slicemerge`	`cms.SliceMerge`	merge with order-insensitive
`mapcopy`	`cms.MapCopy`	copy elem by key
`mapmerge`	`cms.MapMerge`	merge map deeply
...

*: the flag is on by default.

Notes About `DeepCopy()`

Many settings are accumulated in multiple calling on DeepCopy(), such as converters, ignoreNames, and so on. The underlying object is DefaultCopyController.

To get a fresh clean copier, New() or NewFlatDeepCopier() are the choices. BTW, sometimes evendeep.ResetDefaultCopyController() might be helpful.

The only exception is copy-n-merge strategies. There flags are saved and restored on each calling on DeepCopy().

Notes About Global Settings

Some settings are global and available to both of DeepCopy() and New().CopyTo(), such as:

WithStringMarshaller or RegisterDefaultStringMarshaller()
RegisterDefaultConverters
RegisterDefaultCopiers

And so on.

deepcopy

Usages

deepcopy

Getting Started

Customizing The Field Extractor

Customizing The Target Setter

`ByOrdinal` or `ByName`

Customizing A Converter

Zero Target Fields If Equals To Source

Keep The Target Value If Source Is Empty

String Marshalling

Specify CopyMergeStrategy via struct Tag

Name conversions

Sample codes

Strategy Names

Notes About `DeepCopy()`

Notes About Global Settings

On this page

deepcopy

Usages

deepcopy

Getting Started

Customizing The Field Extractor

Customizing The Target Setter

`ByOrdinal` or `ByName`

Customizing A Converter

Zero Target Fields If Equals To Source

Keep The Target Value If Source Is Empty

String Marshalling

Specify CopyMergeStrategy via struct Tag

Name conversions

Sample codes

Strategy Names

Notes About `DeepCopy()`

Notes About Global Settings

On this page