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/*
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 *  This file is part of CoCalc: Copyright © 2020 Sagemath, Inc.
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 *  License: MS-RSL – see LICENSE.md for details
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 */
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import { Assign } from "utility-types";
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import { Restrict, Optionals } from "./types";
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/**
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 * Given an object: T with some optional parameters
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 * and defaults: a subset of optional parameters from T.
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 *
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 * Explicitly setting a default to `undefined` is not recommended
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 *
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 * @return T except provided defaults are guaranteed
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 *
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 * @example
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 *     props: {foo: string; bar?: string},
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 *     defaults: {bar: "good stuff"}
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 *        => {foo: string; bar: string} // <- Note bar is defined
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 *
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 *
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 *     props: {foo: string; bar?: string; baz?: number},
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 *     defaults: {bar: "good stuff"}
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 *        => {foo: string; bar: string; baz?: number} // <- Note baz is optional
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 * .
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 **/
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export function fill<T extends object, U extends Optionals<T>>(
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  props: T,
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  defaults: Restrict<U, Optionals<T>, "Defaults cannot contain required values">
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): Assign<T, U> {
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  const ret: U = {} as any;
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  for (const key in defaults) {
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    if (!props.hasOwnProperty(key) || props[key] == undefined) {
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      ret[key] = defaults[key];
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    }
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  }
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  return Object.assign({}, props, ret);
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}
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