optional

README

optional.go

optional.go is a simple and generic wrapper around a value and a presence flag inspired by C++'s std::optional.

Installation

go get github.com/JonasMuehlmann/optional.go

How to use

This project exports the package optional, whose only exported entity is the generic Optional struct.

The Optional type implements several convenience methods and standard library interfaces( e.g json and SQL conversions).

To see the implemented methods and interfaces, refer to the documentation available at https://pkg.go.dev/github.com/JonasMuehlmann/optional.go.

Documentation

Overview

optional.go is a simple wrapper around a value and a presence flag

Index

• type Optional
  • func Make[T any](wrappee T) Optional[T]
  • func (optional Optional[T]) GetOrAlternative(alternative T) T
  • func (optional Optional[T]) GetOrDefault(alternative T) T
  • func (optional Optional[T]) GetOrGenerate(alternative func() T) T
  • func (optional Optional[T]) GetTransformedOrEmpty(transformer func(T) any) Optional[any]
  • func (optional Optional[T]) GetTransformedOrSelf(transformer func(T) T) Optional[T]
  • func (optional Optional[T]) IsZero() bool
  • func (optional Optional[T]) MarshalCSV() (string, error)
  • func (optional Optional[T]) MarshalJSON() ([]byte, error)
  • func (optional *Optional[T]) MarshalText() (text []byte, err error)
  • func (optional Optional[T]) Match(someHandler func(T), noneHandler func(T))
  • func (optional *Optional[T]) Scan(value any) error
  • func (optional *Optional[T]) Set(val T)
  • func (optional Optional[T]) String() string
  • func (optional *Optional[T]) UnmarshalCSV(val string) error
  • func (optional *Optional[T]) UnmarshalJSON(input []byte) error
  • func (optional *Optional[T]) UnmarshalText(text []byte) error
  • func (optional *Optional[T]) Unset() T
  • func (optional Optional[T]) Value() (driver.Value, error)

Types

type Optional

type Optional[T any] struct {
	Wrappee  T    `json:"wrapee" db:"wrapee"`
	HasValue bool `json:"has_value" db:"has_value"`
}

Optional holds a Wrappe and a flag indicating the existence or abscence of the Wrapee.

func Make

func Make[T any](wrappee T) Optional[T]

Make creates an optional holding the specified wrappee and sets the HasValue flag to true.

func (Optional[T]) GetOrAlternative

func (optional Optional[T]) GetOrAlternative(alternative T) T

GetOrAlternative returns the Wrapee if the HasValue flag is true, otherwise alternative is returned.

func (Optional[T]) GetOrDefault

func (optional Optional[T]) GetOrDefault(alternative T) T

GetOrDefualt returns the Wrapee if the HasValue flag is true, otherwise T's default value is returned.

func (Optional[T]) GetOrGenerate

func (optional Optional[T]) GetOrGenerate(alternative func() T) T

GetOrGenerate returns the Wrapee if the HasValue flag is true, otherwise the result of alternative() is returned.

func (Optional[T]) GetTransformedOrEmpty

func (optional Optional[T]) GetTransformedOrEmpty(transformer func(T) any) Optional[any]

GetTransformedOrEmpty returns transformer(Wrappee) if HasValue == true, otherwise returns an empty Optional.

func (Optional[T]) GetTransformedOrSelf

func (optional Optional[T]) GetTransformedOrSelf(transformer func(T) T) Optional[T]

GetTransformedOrEmpty returns transformer(Wrappee) if HasValue == true, otherwise returns self.

func (Optional[T]) IsZero

func (optional Optional[T]) IsZero() bool

func (Optional[T]) MarshalCSV

func (optional Optional[T]) MarshalCSV() (string, error)

MarshalCSV implements the gocarina/gocsv.TypeMarshaller interface.

func (Optional[T]) MarshalJSON

func (optional Optional[T]) MarshalJSON() ([]byte, error)

func (*Optional[T]) MarshalText

func (optional *Optional[T]) MarshalText() (text []byte, err error)

MarshalText implements the encoding.TextMarshaller interface.

func (Optional[T]) Match

func (optional Optional[T]) Match(someHandler func(T), noneHandler func(T))

Match executes someHandler if HasValue is true and noneHandler otherwise.

func (*Optional[T]) Scan

func (optional *Optional[T]) Scan(value any) error

Scan implements the database.sql.Scanner interface.

func (*Optional[T]) Set

func (optional *Optional[T]) Set(val T)

Set sets a Wrappee to val value and the HasValue flag to true.

func (Optional[T]) String

func (optional Optional[T]) String() string

String implements the fmt.Stringer interface.

func (*Optional[T]) UnmarshalCSV

func (optional *Optional[T]) UnmarshalCSV(val string) error

UnmarshalCSV implements the gocarina/gocsv.TypeUnmarshaller interface.

func (*Optional[T]) UnmarshalJSON

func (optional *Optional[T]) UnmarshalJSON(input []byte) error

func (*Optional[T]) UnmarshalText

func (optional *Optional[T]) UnmarshalText(text []byte) error

UnmarshalText implements the encoding.TextUnmarshaller interface.

func (*Optional[T]) Unset

func (optional *Optional[T]) Unset() T

Unset sets the HasValue flag to false and returns the Wrappee.

func (Optional[T]) Value

func (optional Optional[T]) Value() (driver.Value, error)

Value implements the database.sql.driver.Valuer interface.