/**
 * This module is not part of the public API!
 */
/**
 * Type that consists of the union of all properties that are marked as optional through a question mark.
 *
 * Note that properties that have undefined in their domain, but no question mark next to the property name are *not*
 * included. Also note that, in strict compilation mode, TypeScript will add undefined to the domain of the property if
 * there is a question mark next to the property name.
 *
 * @typeparam T generic type parameter
 */
export declare type OptionalPropertyNames<T extends {}> = {
    [K in keyof T]-?: {} extends {
        [_ in K]: T[K];
    } ? K : never;
}[keyof T];
export declare type Defined<T> = T extends undefined ? never : T;
export declare type OnlyOptionals<T extends {}> = {
    [K in OptionalPropertyNames<T>]: Defined<T[K]>;
};
/**
 * Copy the values of all string-keyed enumerable own properties from the source object to the target object.
 *
 * Note the differences to
 * [`Object.assign()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign):
 * - Only properties with `string` keys are copied.
 * - A property of the source value that has the value `undefined` is copied only if the property key is not yet in the
 *   target. (The check is performed using the `in` operator.)
 *
 * @param target the target object
 * @param source the source object
 * @return the target object
 */
export declare function assignDefined<T extends {
    [key: string]: any;
}, U extends {
    [key: string]: any;
}>(target: T, source: U | undefined): T & U;
/**
 * Returns a deep clone of the given object.
 *
 * This function covers only what is needed in this project! It is not an equivalent to a library function.
 */
export declare function deepClone<T>(original: T): T;
/**
 * Returns the first argument that is defined, or undefined if none of the arguments is defined.
 */
export declare function coalesce<T>(left: T | undefined, right: T): T;
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