structs

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 Go to latest Published: Aug 3, 2021 License: MIT, MIT Imports: 4 Imported by: 0

README

Structs GoDoc Build Status Coverage Status

Structs contains various utilities to work with Go (Golang) structs. It was initially used by me to convert a struct into a map[string]interface{}. With time I've added other utilities for structs. It's basically a high level package based on primitives from the reflect package. Feel free to add new functions or improve the existing code.

Install

go get github.com/fatih/structs

Usage and Examples

Just like the standard lib strings, bytes and co packages, structs has many global functions to manipulate or organize your struct data. Lets define and declare a struct:

type Server struct {
	Name        string `json:"name,omitempty"`
	ID          int
	Enabled     bool
	users       []string // not exported
	http.Server          // embedded
}

server := &Server{
	Name:    "gopher",
	ID:      123456,
	Enabled: true,
}

// Convert a struct to a map[string]interface{}
// => {"Name":"gopher", "ID":123456, "Enabled":true}
m := structs.Map(server)

// Convert the values of a struct to a []interface{}
// => ["gopher", 123456, true]
v := structs.Values(server)

// Convert the names of a struct to a []string
// (see "Names methods" for more info about fields)
n := structs.Names(server)

// Convert the values of a struct to a []*Field
// (see "Field methods" for more info about fields)
f := structs.Fields(server)

// Return the struct name => "Server"
n := structs.Name(server)

// Check if any field of a struct is initialized or not.
h := structs.HasZero(server)

// Check if all fields of a struct is initialized or not.
z := structs.IsZero(server)

// Check if server is a struct or a pointer to struct
i := structs.IsStruct(server)
Struct methods

The structs functions can be also used as independent methods by creating a new *structs.Struct. This is handy if you want to have more control over the structs (such as retrieving a single Field).

// Create a new struct type:
s := structs.New(server)

m := s.Map()              // Get a map[string]interface{}
v := s.Values()           // Get a []interface{}
f := s.Fields()           // Get a []*Field
n := s.Names()            // Get a []string
f := s.Field(name)        // Get a *Field based on the given field name
f, ok := s.FieldOk(name)  // Get a *Field based on the given field name
n := s.Name()             // Get the struct name
h := s.HasZero()          // Check if any field is initialized
z := s.IsZero()           // Check if all fields are initialized
Field methods

We can easily examine a single Field for more detail. Below you can see how we get and interact with various field methods:

s := structs.New(server)

// Get the Field struct for the "Name" field
name := s.Field("Name")

// Get the underlying value,  value => "gopher"
value := name.Value().(string)

// Set the field's value
name.Set("another gopher")

// Get the field's kind, kind =>  "string"
name.Kind()

// Check if the field is exported or not
if name.IsExported() {
	fmt.Println("Name field is exported")
}

// Check if the value is a zero value, such as "" for string, 0 for int
if !name.IsZero() {
	fmt.Println("Name is initialized")
}

// Check if the field is an anonymous (embedded) field
if !name.IsEmbedded() {
	fmt.Println("Name is not an embedded field")
}

// Get the Field's tag value for tag name "json", tag value => "name,omitempty"
tagValue := name.Tag("json")

Nested structs are supported too:

addrField := s.Field("Server").Field("Addr")

// Get the value for addr
a := addrField.Value().(string)

// Or get all fields
httpServer := s.Field("Server").Fields()

We can also get a slice of Fields from the Struct type to iterate over all fields. This is handy if you wish to examine all fields:

s := structs.New(server)

for _, f := range s.Fields() {
	fmt.Printf("field name: %+v\n", f.Name())

	if f.IsExported() {
		fmt.Printf("value   : %+v\n", f.Value())
		fmt.Printf("is zero : %+v\n", f.IsZero())
	}
}

Credits

License

The MIT License (MIT) - see LICENSE.md for more details

Documentation

Overview

Package structs contains various utilities functions to work with structs.

Index

Examples

Constants

This section is empty.

Variables

View Source 
var (
	// DefaultTagName is the default tag name for struct fields which provides
	// a more granular to tweak certain structs. Lookup the necessary functions
	// for more info.
	DefaultTagName = "structs" // struct's field default tag name
)

Functions

func FillMap 

func FillMap(s interface{}, out map[string]interface{})

FillMap is the same as Map. Instead of returning the output, it fills the given map.

func HasZero 

func HasZero(s interface{}) bool

HasZero returns true if any field is equal to a zero value. For more info refer to Struct types HasZero() method. It panics if s's kind is not struct.

Example 
// Let's define an Access struct. Note that the "Enabled" field is not
// going to be checked because we added the "structs" tag to the field.
type Access struct {
	Name         string
	LastAccessed time.Time
	Number       int
	Enabled      bool `structs:"-"`
}

// Name and Number is not initialized.
a := &Access{
	LastAccessed: time.Now(),
}
hasZeroA := HasZero(a)

// Name and Number is initialized.
b := &Access{
	Name:         "Fatih",
	LastAccessed: time.Now(),
	Number:       12345,
}
hasZeroB := HasZero(b)

fmt.Printf("%#v\n", hasZeroA)
fmt.Printf("%#v\n", hasZeroB)

Output:

true
false

func IsStruct 

func IsStruct(s interface{}) bool

IsStruct returns true if the given variable is a struct or a pointer to struct.

func IsZero 

func IsZero(s interface{}) bool

IsZero returns true if all fields is equal to a zero value. For more info refer to Struct types IsZero() method. It panics if s's kind is not struct.

Example 
type Server struct {
	Name    string
	ID      int32
	Enabled bool
}

// Nothing is initalized
a := &Server{}
isZeroA := IsZero(a)

// Name and Enabled is initialized, but not ID
b := &Server{
	Name:    "Golang",
	Enabled: true,
}
isZeroB := IsZero(b)

fmt.Printf("%#v\n", isZeroA)
fmt.Printf("%#v\n", isZeroB)

Output:

true
false

func Map 

func Map(s interface{}) map[string]interface{}

Map converts the given struct to a map[string]interface{}. For more info refer to Struct types Map() method. It panics if s's kind is not struct.

Example 
type Server struct {
	Name    string
	ID      int32
	Enabled bool
}

s := &Server{
	Name:    "Arslan",
	ID:      123456,
	Enabled: true,
}

m := Map(s)

fmt.Printf("%#v\n", m["Name"])
fmt.Printf("%#v\n", m["ID"])
fmt.Printf("%#v\n", m["Enabled"])

Output:

"Arslan"
123456
true
Example (OmitEmpty) 
// By default field with struct types of zero values are processed too. We
// can stop processing them via "omitempty" tag option.
type Server struct {
	Name     string `structs:",omitempty"`
	ID       int32  `structs:"server_id,omitempty"`
	Location string
}

// Only add location
s := &Server{
	Location: "Tokyo",
}

m := Map(s)

// map contains only the Location field
fmt.Printf("%v\n", m)

Output:

map[Location:Tokyo]
Example (OmitNested) 
// By default field with struct types are processed too. We can stop
// processing them via "omitnested" tag option.
type Server struct {
	Name string    `structs:"server_name"`
	ID   int32     `structs:"server_id"`
	Time time.Time `structs:"time,omitnested"` // do not convert to map[string]interface{}
}

const shortForm = "2006-Jan-02"
t, _ := time.Parse("2006-Jan-02", "2013-Feb-03")

s := &Server{
	Name: "Zeynep",
	ID:   789012,
	Time: t,
}

m := Map(s)

// access them by the custom tags defined above
fmt.Printf("%v\n", m["server_name"])
fmt.Printf("%v\n", m["server_id"])
fmt.Printf("%v\n", m["time"].(time.Time))

Output:

Zeynep
789012
2013-02-03 00:00:00 +0000 UTC
Example (Tags) 
// Custom tags can change the map keys instead of using the fields name
type Server struct {
	Name    string `structs:"server_name"`
	ID      int32  `structs:"server_id"`
	Enabled bool   `structs:"enabled"`
}

s := &Server{
	Name: "Zeynep",
	ID:   789012,
}

m := Map(s)

// access them by the custom tags defined above
fmt.Printf("%#v\n", m["server_name"])
fmt.Printf("%#v\n", m["server_id"])
fmt.Printf("%#v\n", m["enabled"])

Output:

"Zeynep"
789012
false

func Name 

func Name(s interface{}) string

Name returns the structs's type name within its package. It returns an empty string for unnamed types. It panics if s's kind is not struct.

func Names 

func Names(s interface{}) []string

Names returns a slice of field names. For more info refer to Struct types Names() method. It panics if s's kind is not struct.

func Values 

func Values(s interface{}) []interface{}

Values converts the given struct to a []interface{}. For more info refer to Struct types Values() method. It panics if s's kind is not struct.

Example 
type Server struct {
	Name    string
	ID      int32
	Enabled bool
}

s := &Server{
	Name:    "Fatih",
	ID:      135790,
	Enabled: false,
}

m := Values(s)

fmt.Printf("Values: %+v\n", m)

Output:

Values: [Fatih 135790 false]
Example (OmitEmpty) 
// By default field with struct types of zero values are processed too. We
// can stop processing them via "omitempty" tag option.
type Server struct {
	Name     string `structs:",omitempty"`
	ID       int32  `structs:"server_id,omitempty"`
	Location string
}

// Only add location
s := &Server{
	Location: "Ankara",
}

m := Values(s)

// values contains only the Location field
fmt.Printf("Values: %+v\n", m)

Output:

Values: [Ankara]
Example (Tags) 
type Location struct {
	City    string
	Country string
}

type Server struct {
	Name     string
	ID       int32
	Enabled  bool
	Location Location `structs:"-"` // values from location are not included anymore
}

s := &Server{
	Name:     "Fatih",
	ID:       135790,
	Enabled:  false,
	Location: Location{City: "Ankara", Country: "Turkey"},
}

// Let get all values from the struct s. Note that we don't include values
// from the Location field
m := Values(s)

fmt.Printf("Values: %+v\n", m)

Output:

Values: [Fatih 135790 false]

Types

type Field 

type Field struct {
	// contains filtered or unexported fields
}

Field represents a single struct field that encapsulates high level functions around the field.

Example 
type Person struct {
	Name   string
	Number int
}

type Access struct {
	Person        Person
	HasPermission bool
	LastAccessed  time.Time
}

access := &Access{
	Person:        Person{Name: "fatih", Number: 1234567},
	LastAccessed:  time.Now(),
	HasPermission: true,
}

// Create a new Struct type
s := New(access)

// Get the Field type for "Person" field
p := s.Field("Person")

// Get the underlying "Name field" and print the value of it
name := p.Field("Name")

fmt.Printf("Value of Person.Access.Name: %+v\n", name.Value())

Output:

Value of Person.Access.Name: fatih

func Fields 

func Fields(s interface{}) []*Field

Fields returns a slice of *Field. For more info refer to Struct types Fields() method. It panics if s's kind is not struct.

Example 
type Access struct {
	Name         string
	LastAccessed time.Time
	Number       int
}

s := &Access{
	Name:         "Fatih",
	LastAccessed: time.Now(),
	Number:       1234567,
}

fields := Fields(s)

for i, field := range fields {
	fmt.Printf("[%d] %+v\n", i, field.Name())
}

Output:

[0] Name
[1] LastAccessed
[2] Number
Example (Nested) 
type Person struct {
	Name   string
	Number int
}

type Access struct {
	Person        Person
	HasPermission bool
	LastAccessed  time.Time
}

s := &Access{
	Person:        Person{Name: "fatih", Number: 1234567},
	LastAccessed:  time.Now(),
	HasPermission: true,
}

// Let's get all fields from the struct s.
fields := Fields(s)

for _, field := range fields {
	if field.Name() == "Person" {
		fmt.Printf("Access.Person.Name: %+v\n", field.Field("Name").Value())
	}
}

Output:

Access.Person.Name: fatih

func (*Field) Field 

func (f *Field) Field(name string) *Field

Field returns the field from a nested struct. It panics if the nested struct is not exported or if the field was not found.

func (*Field) FieldOk 

func (f *Field) FieldOk(name string) (*Field, bool)

FieldOk returns the field from a nested struct. The boolean returns whether the field was found (true) or not (false).

func (*Field) Fields 

func (f *Field) Fields() []*Field

Fields returns a slice of Fields. This is particular handy to get the fields of a nested struct . A struct tag with the content of "-" ignores the checking of that particular field. Example: 

// Field is ignored by this package.
Field *http.Request `structs:"-"`

It panics if field is not exported or if field's kind is not struct

func (*Field) IsEmbedded 

func (f *Field) IsEmbedded() bool

IsEmbedded returns true if the given field is an anonymous field (embedded)

func (*Field) IsExported 

func (f *Field) IsExported() bool

IsExported returns true if the given field is exported.

func (*Field) IsZero 

func (f *Field) IsZero() bool

IsZero returns true if the given field is not initialized (has a zero value). It panics if the field is not exported.

func (*Field) Kind 

func (f *Field) Kind() reflect.Kind

Kind returns the fields kind, such as "string", "map", "bool", etc ..

func (*Field) Name 

func (f *Field) Name() string

Name returns the name of the given field

func (*Field) Set 

func (f *Field) Set(val interface{}) error

Set sets the field to given value v. It returns an error if the field is not settable (not addressable or not exported) or if the given value's type doesn't match the fields type.

func (*Field) Tag 

func (f *Field) Tag(key string) string

Tag returns the value associated with key in the tag string. If there is no such key in the tag, Tag returns the empty string.

func (*Field) Value 

func (f *Field) Value() interface{}

Value returns the underlying value of the field. It panics if the field is not exported.

func (*Field) Zero 

func (f *Field) Zero() error

Zero sets the field to its zero value. It returns an error if the field is not settable (not addressable or not exported).

type Struct 

type Struct struct {
	TagName string
	// contains filtered or unexported fields
}

Struct encapsulates a struct type to provide several high level functions around the struct.

func New 

func New(s interface{}) *Struct

New returns a new *Struct with the struct s. It panics if the s's kind is not struct.

Example 
type Server struct {
	Name    string
	ID      int32
	Enabled bool
}

server := &Server{
	Name:    "Arslan",
	ID:      123456,
	Enabled: true,
}

s := New(server)

fmt.Printf("Name        : %v\n", s.Name())
fmt.Printf("Values      : %v\n", s.Values())
fmt.Printf("Value of ID : %v\n", s.Field("ID").Value())

Output:

Name        : Server
Values      : [Arslan 123456 true]
Value of ID : 123456

func (*Struct) Field 

func (s *Struct) Field(name string) *Field

Field returns a new Field struct that provides several high level functions around a single struct field entity. It panics if the field is not found.

func (*Struct) FieldOk 

func (s *Struct) FieldOk(name string) (*Field, bool)

FieldOk returns a new Field struct that provides several high level functions around a single struct field entity. The boolean returns true if the field was found.

func (*Struct) Fields 

func (s *Struct) Fields() []*Field

Fields returns a slice of Fields. A struct tag with the content of "-" ignores the checking of that particular field. Example: 

// Field is ignored by this package.
Field bool `structs:"-"`

It panics if s's kind is not struct.

func (*Struct) FillMap 

func (s *Struct) FillMap(out map[string]interface{})

FillMap is the same as Map. Instead of returning the output, it fills the given map.

func (*Struct) HasZero 

func (s *Struct) HasZero() bool

HasZero returns true if a field in a struct is not initialized (zero value). A struct tag with the content of "-" ignores the checking of that particular field. Example: 

// Field is ignored by this package.
Field bool `structs:"-"`

A value with the option of "omitnested" stops iterating further if the type is a struct. Example: 

// Field is not processed further by this package.
Field time.Time     `structs:"myName,omitnested"`
Field *http.Request `structs:",omitnested"`

Note that only exported fields of a struct can be accessed, non exported fields will be neglected. It panics if s's kind is not struct.

func (*Struct) IsZero 

func (s *Struct) IsZero() bool

IsZero returns true if all fields in a struct is a zero value (not initialized) A struct tag with the content of "-" ignores the checking of that particular field. Example: 

// Field is ignored by this package.
Field bool `structs:"-"`

A value with the option of "omitnested" stops iterating further if the type is a struct. Example: 

// Field is not processed further by this package.
Field time.Time     `structs:"myName,omitnested"`
Field *http.Request `structs:",omitnested"`

Note that only exported fields of a struct can be accessed, non exported fields will be neglected. It panics if s's kind is not struct.

func (*Struct) Map 

func (s *Struct) Map() map[string]interface{}

Map converts the given struct to a map[string]interface{}, where the keys of the map are the field names and the values of the map the associated values of the fields. The default key string is the struct field name but can be changed in the struct field's tag value. The "structs" key in the struct's field tag value is the key name. Example: 

// Field appears in map as key "myName".
Name string `structs:"myName"`

A tag value with the content of "-" ignores that particular field. Example: 

// Field is ignored by this package.
Field bool `structs:"-"`

A tag value with the content of "string" uses the stringer to get the value. Example: 

// The value will be output of Animal's String() func.
// Map will panic if Animal does not implement String().
Field *Animal `structs:"field,string"`

A tag value with the option of "flatten" used in a struct field is to flatten its fields in the output map. Example: 

// The FieldStruct's fields will be flattened into the output map.
FieldStruct time.Time `structs:",flatten"`

A tag value with the option of "omitnested" stops iterating further if the type is a struct. Example: 

// Field is not processed further by this package.
Field time.Time     `structs:"myName,omitnested"`
Field *http.Request `structs:",omitnested"`

A tag value with the option of "omitempty" ignores that particular field if the field value is empty. Example: 

// Field appears in map as key "myName", but the field is
// skipped if empty.
Field string `structs:"myName,omitempty"`

// Field appears in map as key "Field" (the default), but
// the field is skipped if empty.
Field string `structs:",omitempty"`

Note that only exported fields of a struct can be accessed, non exported fields will be neglected.

func (*Struct) Name 

func (s *Struct) Name() string

Name returns the structs's type name within its package. For more info refer to Name() function.

func (*Struct) Names 

func (s *Struct) Names() []string

Names returns a slice of field names. A struct tag with the content of "-" ignores the checking of that particular field. Example: 

// Field is ignored by this package.
Field bool `structs:"-"`

It panics if s's kind is not struct.

func (*Struct) Values 

func (s *Struct) Values() []interface{}

Values converts the given s struct's field values to a []interface{}. A struct tag with the content of "-" ignores the that particular field. Example: 

// Field is ignored by this package.
Field int `structs:"-"`

A value with the option of "omitnested" stops iterating further if the type is a struct. Example: 

// Fields is not processed further by this package.
Field time.Time     `structs:",omitnested"`
Field *http.Request `structs:",omitnested"`

A tag value with the option of "omitempty" ignores that particular field and is not added to the values if the field value is empty. Example: 

// Field is skipped if empty
Field string `structs:",omitempty"`

Note that only exported fields of a struct can be accessed, non exported fields will be neglected.

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