opt

Install: go get -u github.com/ifnotnil/opt

Golang generic optional type with support for json.Marshaler, json.Unmarshaler, driver.Valuer, sql.Scanner and golang 1.24 json omitzero tag.

The main ideas are:

• Separate present-but-nil from not present (e.g., for the HTTP PATCH method).
• Implement optional values without using pointers.

States

State	Constructor function	Description
None	None[T]()	Value is absent, not preset nor nil.
Nil	Nil[T]()	Value is present but nil
Valid	New[T](t T)	Value is preset and valid (not nil)

Json unmarshaling

Given a struct

type Foo struct {
	A Optional[int] `json:"a"`
}

Json	Resulted state of A
{}	None
{"a": null}	Nil
{"a": 123}	Valid

Why not Set?

We can achieve that by writing the optional value using one of the constructor functions.

a := Nil["string")
// ...

a = New("test")