field

Documentation

Overview

Package field provides some functions about the struct field.

Index

• func GetAllFields(stype reflect.Type) []reflect.StructField
• func GetAllFieldsWithTag(stype reflect.Type, tag string) map[string]Field
• func GetTag(sf reflect.StructField, tag string) (value, arg string)
• func GetValueByName(structValue interface{}, fieldName string) (fieldValue reflect.Value, ok bool)
• func LookupTag(sf reflect.StructField, tag string) (value, arg string, ok bool)
• type Field

Examples

• GetAllFields
• GetAllFieldsWithTag
• GetTag
• GetValueByName

Functions

func GetAllFields

func GetAllFields(stype reflect.Type) []reflect.StructField

GetAllFields returns all the field types of the struct.

Example

type Uint uint
var s struct {
	string
	Uint

	str string
	Int int
}

fields := GetAllFields(reflect.TypeOf(s))
for _, field := range fields {
	fmt.Printf("name=%s, isexported=%v, anonymous=%v\n",
		field.Name, field.IsExported(), field.Anonymous)
}

Output:

name=string, isexported=false, anonymous=true
name=Uint, isexported=true, anonymous=true
name=str, isexported=false, anonymous=false
name=Int, isexported=true, anonymous=false

func GetAllFieldsWithTag

func GetAllFieldsWithTag(stype reflect.Type, tag string) map[string]Field

GetAllFieldsWithTag returns all the field types of the struct with the tag, which will filter the fields that the tag value contains "-".

Example

type Uint uint
var s struct {
	string
	Uint

	str string
	Int int64 `json:"int64"`

	int    `json:"-"`
	Ignore int `json:"-"`
}

fields := GetAllFieldsWithTag(reflect.TypeOf(s), "json")
for name, field := range fields {
	fmt.Printf("name=%s, isexported=%v, anonymous=%v\n",
		name, field.IsExported(), field.Anonymous)
}

Output:

name=string, isexported=false, anonymous=true
name=Uint, isexported=true, anonymous=true
name=str, isexported=false, anonymous=false
name=int64, isexported=true, anonymous=false

func GetTag

func GetTag(sf reflect.StructField, tag string) (value, arg string)

GetTag returns the value and arg about the tag from the struct field.

Example

type T struct {
	Int   int
	Int8  int8  `key:""`
	Int16 int16 `key:"int16"`
	Int32 int32 `key:",arg"`
	Int64 int64 `key:"int64,arg"`
	Bool  bool  `key:"-"`
}

stype := reflect.TypeOf(T{})
for i := 0; i < stype.NumField(); i++ {
	field := stype.Field(i)
	value, arg := GetTag(field, "key")
	fmt.Printf("fieldname=%s, tagvalue=%s, tagarg=%s\n", field.Name, value, arg)
}

Output:

fieldname=Int, tagvalue=, tagarg=
fieldname=Int8, tagvalue=, tagarg=
fieldname=Int16, tagvalue=int16, tagarg=
fieldname=Int32, tagvalue=, tagarg=arg
fieldname=Int64, tagvalue=int64, tagarg=arg
fieldname=Bool, tagvalue=-, tagarg=

func GetValueByName

func GetValueByName(structValue interface{}, fieldName string) (fieldValue reflect.Value, ok bool)

GetValueByName returns the struct field value by the name.

fieldName maybe starts with ".".

Example

print := func(v interface{}, name string) {
	if vf, ok := GetValueByName(v, name); ok {
		fmt.Printf("%s: %v\n", name, vf.Interface())
	} else {
		fmt.Printf("no the field named \"%s\"\n", name)
	}
}

var v struct {
	Field1 int
	Field2 string
	Field3 struct {
		Field4 int
		Field5 string
		Field6 struct {
			Field7 int
			Field8 string
		}
	}
}
v.Field1 = 123
v.Field2 = "abc"
v.Field3.Field4 = 456
v.Field3.Field5 = "rst"
v.Field3.Field6.Field7 = 789
v.Field3.Field6.Field8 = "xyz"

fmt.Println("--- Struct ---")
print(v, ".Field1")
print(v, "Field2")
print(v, "Field4")
print(v, "Field3.Field4")
print(v, "Field3.Field7")
print(v, "Field3.Field6.Field7")
print(v, "Field3.Field6.Field9")

fmt.Println()
fmt.Println("--- Pointer to Struct ---")
print(&v, ".Field1")
print(&v, "Field2")
print(&v, "Field4")
print(&v, "Field3.Field4")
print(&v, "Field3.Field7")
print(&v, "Field3.Field6.Field7")
print(&v, "Field3.Field6.Field9")

fmt.Println()
fmt.Println("--- reflect.Value of Struct ---")
print(reflect.ValueOf(v), ".Field1")
print(reflect.ValueOf(v), "Field2")
print(reflect.ValueOf(v), "Field4")
print(reflect.ValueOf(v), "Field3.Field4")
print(reflect.ValueOf(v), "Field3.Field7")
print(reflect.ValueOf(v), "Field3.Field6.Field7")
print(reflect.ValueOf(v), "Field3.Field6.Field9")

fmt.Println()
fmt.Println("--- reflect.Value of Pointer to Struct ---")
print(reflect.ValueOf(&v), ".Field1")
print(reflect.ValueOf(&v), "Field2")
print(reflect.ValueOf(&v), "Field4")
print(reflect.ValueOf(&v), "Field3.Field4")
print(reflect.ValueOf(&v), "Field3.Field7")
print(reflect.ValueOf(&v), "Field3.Field6.Field7")
print(reflect.ValueOf(&v), "Field3.Field6.Field9")

Output:

--- Struct ---
.Field1: 123
Field2: abc
no the field named "Field4"
Field3.Field4: 456
no the field named "Field3.Field7"
Field3.Field6.Field7: 789
no the field named "Field3.Field6.Field9"

--- Pointer to Struct ---
.Field1: 123
Field2: abc
no the field named "Field4"
Field3.Field4: 456
no the field named "Field3.Field7"
Field3.Field6.Field7: 789
no the field named "Field3.Field6.Field9"

--- reflect.Value of Struct ---
.Field1: 123
Field2: abc
no the field named "Field4"
Field3.Field4: 456
no the field named "Field3.Field7"
Field3.Field6.Field7: 789
no the field named "Field3.Field6.Field9"

--- reflect.Value of Pointer to Struct ---
.Field1: 123
Field2: abc
no the field named "Field4"
Field3.Field4: 456
no the field named "Field3.Field7"
Field3.Field6.Field7: 789
no the field named "Field3.Field6.Field9"

func LookupTag

func LookupTag(sf reflect.StructField, tag string) (value, arg string, ok bool)

LookupTag returns the value and arg about the tag from the struct field.

Types

type Field

type Field struct {
	reflect.StructField
	FieldName string // If TagName is not empty, it is equal to TagName. Or, StructField.Name.
	TagValue  string
	TagArg    string
	Index     int
}

Field represents the information of the struct field.