# Optimistic

Represents an optimistic value together with the exact state it replaced.

## Signatures

```ts
export interface Optimistic<A, E> {
    readonly _tag: "Optimistic";
    readonly value: A;
    readonly previous: AsyncData<A, E>;
}
```

## Why

Preserving history makes rollback and nested optimistic transformations explicit rather than hiding them in renderer state.

## Ownership and lifetime

This plain wrapper acquires no resources and retains its previous state; `readonly` is compile-time only.

## Property: _tag

The discriminant for optimistic state.

## Property: _tag: Why

The literal tag enables explicit optimistic handling and cycle-safe traversal.

## Property: _tag: Ownership and lifetime

Inherits the resource-free lifetime of its enclosing state.

## Property: previous

The state to restore or inspect beneath this optimistic layer.

## Property: previous: Why

Explicit history supports deterministic rollback and transformation of nested optimistic states.

## Property: previous: Ownership and lifetime

Inherits the enclosing optimistic wrapper's resource-free lifetime.

## Property: value

The value currently presented optimistically.

## Property: value: Why

Separating the provisional value from history makes pending intent directly observable.

## Property: value: Ownership and lifetime

Inherits the enclosing state's lifetime; the caller retains ownership of the referenced value.

## Examples

```ts
import { optimistic, success } from "@typed/async-data"
const state = optimistic(success(1), 2)
```