structs

-- import "."

Package structs contains various utilities to work with Go (Golang) structs. It was initially used by me to convert a struct into a map[string]any. 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 go.devnw.com/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]any

// => {"Name":"gopher", "ID":123456, "Enabled":true} m := structs.Map(server)

// Convert the values of a struct to a []any // => ["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]any v := s.Values() // Get a []any 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 uninitialized z := s.IsZero() // Check if
all fields are uninitialized

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

- [Fatih Arslan](https://github.com/fatih)
- [Cihangir Savas](https://github.com/cihangir)

License

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

Usage

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.
	//nolint:gochecknoglobals // this is a purposeful global
	DefaultTagName = "structs" // struct's field default tag name
)

func FillMap

func FillMap(s any, out map[string]any)

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

func HasZero

func HasZero(s any) 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.

func IsStruct

func IsStruct(s any) bool

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

func IsZero

func IsZero(s any) 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.

func Map

func Map(s any) map[string]any

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

func Name

func Name(s any) 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 any) []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 any) []any

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

type Field

type Field struct {
}

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

func Fields

func Fields(s any) []*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.

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 any) 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() any

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
}

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

func New

func New(s any) *Struct

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

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]any)

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]any

Map converts the given struct to a map[string]any, 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() []any

Values converts the given s struct's field values to a []any. 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.