import { Boxed, ValidationErrors } from 'ngrx-forms';
export interface NumberValidationError<T> {
    actual: T;
}
declare module 'ngrx-forms' {
    interface ValidationErrors {
        number?: NumberValidationError<any>;
    }
}
/**
 * A validation function that requires a value to be a valid number.
 * Considers `null` and `undefined` as valid. Combine this function with the
 * `required` validation function if these values should be considered invalid.
 *
 * The validation error returned by this validation function has the following shape:
 *
```typescript
{
  number: {
    actual: any;
  };
}
```
 *
 * Usually you would use this validation function in conjunction with the `validate`
 * update function to perform synchronous validation in your reducer:
 *
```typescript
updateGroup<MyFormValue>({
  amount: validate(number),
})
```
 *
 * Note that this function is generic to allow the compiler to properly infer the type
 * of the `validate` function for both optional and non-optional controls.
 */
export declare function number<T extends number | Boxed<number> | null | undefined>(value: T): ValidationErrors;