# has

Check if the current state of a RefStruct has a property.

## Signatures

```ts
export declare const has: {
    <S extends object, const K extends keyof S>(key: K): <E, R>(ref: RefStruct<S, E, R>) => RefSubject.Computed<boolean, E, R>;
    <S extends object, const K extends keyof S, E, R>(ref: RefStruct<S, E, R>, key: K): RefSubject.Computed<boolean, E, R>;
};
```

## Why

Makes has a live projection of the struct; consumers can sample it now or observe it without
copying the source state.

## Ownership and lifetime

The has view retains no independent state. An Effect read samples the source once; Fx
observation follows later pushes and its observing Scope owns subscription cleanup.