option.go

package option

import "fmt"

// Option represents an optional value. The [Some] variant contains a value and
// the [None] variant represents the absence of a value.
type Option[T any] struct {
	value   T
	present bool
}

// Some instantiates an [Option] with a value.
func Some[T any](value T) Option[T] {
	return Option[T]{value, true}
}

// None instantiates an [Option] with no value.
func None[T any]() Option[T] {
	return Option[T]{}
}

// String implements the [fmt.Stringer] interface.
func (o Option[T]) String() string {
	if o.present {
		return fmt.Sprintf("Some(%v)", o.value)
	}

	return "None"
}

var _ fmt.Stringer = Option[struct{}]{}

// Unwrap returns the underlying value of a [Some] variant, or panics if called
// on a [None] variant.
func (o Option[T]) Unwrap() T {
	if o.present {
		return o.value
	}

	panic("called `Option.Unwrap()` on a `None` value")
}

// UnwrapOr returns the underlying value of a [Some] variant, or the provided
// value on a [None] variant.
func (o Option[T]) UnwrapOr(value T) T {
	if o.present {
		return o.value
	}

	return value
}

// UnwrapOrElse returns the underlying value of a [Some] variant, or the result
// of calling the provided function on a [None] variant.
func (o Option[T]) UnwrapOrElse(f func() T) T {
	if o.present {
		return o.value
	}

	return f()
}

// UnwrapOrZero returns the underlying value of a [Some] variant, or the zero
// value on a [None] variant.
func (o Option[T]) UnwrapOrZero() T {
	if o.present {
		return o.value
	}

	var value T
	return value
}

// IsSome returns true if the [Option] is a [Some] variant.
func (o Option[T]) IsSome() bool {
	return o.present
}

// IsNone returns true if the [Option] is a [None] variant.
func (o Option[T]) IsNone() bool {
	return !o.present
}

// Value returns the underlying value and true for a [Some] variant, or the
// zero value and false for a [None] variant.
func (o Option[T]) Value() (T, bool) {
	return o.value, o.present
}

// Expect returns the underlying value for a [Some] variant, or panics with the
// provided message for a [None] variant.
func (o Option[T]) Expect(message string) T {
	if o.present {
		return o.value
	}

	panic(message)
}