Define names and lengths for iterator functions

[Pisces] / object.js

// SPDX-FileCopyrightText: 2022, 2023, 2025 Lady <https://www.ladys.computer/about/#lady>
// SPDX-License-Identifier: MPL-2.0
/**
 * ⁌ ♓🧩 Piscēs ∷ object.js
 *
 * Copyright © 2022–2023, 2025 Lady [@ Ladys Computer].
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at <https://mozilla.org/MPL/2.0/>.
 */

import {
  IS_CONCAT_SPREADABLE,
  isAccessorDescriptor,
  isDataDescriptor,
  SPECIES,
  toFunctionName,
  toLength,
  type,
  UNDEFINED,
} from "./value.js";

const PISCĒS = "♓🧩 Piscēs";

const createArray = Array;
const { isArray } = Array;
const object = Object;
const {
  assign,
  create,
  defineProperty,
  defineProperties,
  entries,
  freeze: objectFreeze,
  fromEntries,
  getOwnPropertyDescriptor: objectGetOwnPropertyDescriptor,
  getOwnPropertyNames,
  getOwnPropertySymbols: objectGetOwnPropertySymbols,
  getPrototypeOf,
  hasOwn,
  isExtensible,
  isFrozen,
  isSealed,
  keys,
  preventExtensions: objectPreventExtensions,
  seal: objectSeal,
  setPrototypeOf,
  values,
} = Object;
const {
  apply: call,
  deleteProperty,
  defineProperty: reflectDefineProperty,
  get,
  getOwnPropertyDescriptor: reflectGetOwnPropertyDescriptor,
  has,
  ownKeys,
  set,
  setPrototypeOf: reflectSetPrototypeOf,
} = Reflect;

/**
 * An object whose properties are lazy‐loaded from the methods on the
 * own properties of the provided object.
 *
 * This is useful when you are looking to reference properties on
 * objects which, due to module dependency graphs, cannot be guaranteed
 * to have been initialized yet.
 *
 * The resulting properties will have the same attributes (regarding
 * configurability, enumerability, and writability) as the
 * corresponding properties on the methods object. If a property is
 * marked as writable, the method will never be called if it is set
 * before it is gotten. By necessity, the resulting properties are all
 * configurable before they are accessed for the first time.
 *
 * Methods will be called with the resulting object as their this
 * value.
 *
 * `LazyLoader´ objects have the same prototype as the passed methods
 * object.
 */
export class LazyLoader extends null {
  /**
   * Constructs a new `LazyLoader´ object.
   *
   * ☡ This function throws if the provided value is not an object.
   */
  constructor(loadMethods) {
    if (type(loadMethods) !== "object") {
      // The provided value is not an object; this is an error.
      throw new TypeError(
        `${PISCĒS}: Cannot construct LazyLoader: Provided argument is not an object: ${loadMethods}.`,
      );
    } else {
      // The provided value is an object.
      //
      // Process it and build the result.
      const result = create(getPrototypeOf(loadMethods));
      const methodKeys = ownKeys(loadMethods);
      for (let index = 0; index < methodKeys.length; ++index) {
        // Iterate over the property keys of the provided object and
        // define getters and setters appropriately on the result.
        const methodKey = methodKeys[index];
        const { configurable, enumerable, writable } =
          getOwnPropertyDescriptor(loadMethods, methodKey);
        defineProperty(
          result,
          methodKey,
          assign(create(null), {
            configurable: true,
            enumerable,
            get: defineProperty(
              () => {
                const value = call(loadMethods[methodKey], result, []);
                defineProperty(
                  result,
                  methodKey,
                  assign(create(null), {
                    configurable,
                    enumerable,
                    value,
                    writable,
                  }),
                );
                return value;
              },
              "name",
              assign(create(null), {
                value: toFunctionName(methodKey, "get"),
              }),
            ),
            set: writable
              ? defineProperty(
                ($) =>
                  defineProperty(
                    result,
                    methodKey,
                    assign(create(null), {
                      configurable,
                      enumerable,
                      value: $,
                      writable,
                    }),
                  ),
                "name",
                assign(create(null), {
                  value: toFunctionName(methodKey, "set"),
                }),
              )
              : UNDEFINED,
          }),
        );
      }
      return result;
    }
  }
}

/**
 * Defines an own enumerable data property on the provided object with
 * the provided property key and value.
 */
export const defineOwnDataProperty = (O, P, V) =>
  defineProperty(
    O,
    P,
    assign(create(null), {
      configurable: true,
      enumerable: true,
      value: V,
      writable: true,
    }),
  );

/**
 * Defines an own nonenumerable data property on the provided object
 * with the provided property key and value.
 */
export const defineOwnNonenumerableDataProperty = (O, P, V) =>
  defineProperty(
    O,
    P,
    assign(create(null), {
      configurable: true,
      enumerable: false,
      value: V,
      writable: true,
    }),
  );

/**
 * Defines an own property on the provided object on the provided
 * property key using the provided property descriptor.
 *
 * ※ This is effectively an alias for `Object.defineProperty´.
 */
export const defineOwnProperty = (O, P, Desc) =>
  defineProperty(O, P, Desc);

/**
 * Defines own properties on the provided object using the descriptors
 * on the enumerable own properties of the provided additional objects.
 *
 * ※ This function differs from `Object.defineProperties´ in that it
 * can take multiple source objects.
 */
export const defineOwnProperties = (O, ...sources) => {
  const { length } = sources;
  for (let k = 0; k < length; ++k) {
    // Iterate over each source and define the appropriate properties
    // on the provided object.
    defineProperties(O, sources[k]);
  }
  return O;
};

/**
 * Removes the provided property key from the provided object and
 * returns the object.
 *
 * ※ This function differs from `Reflect.deleteProperty´ and the
 * `delete´ operator in that it throws if the deletion is
 * unsuccessful.
 *
 * ☡ This function throws if the first argument is not an object.
 */
export const deleteOwnProperty = (O, P) => {
  if (type(O) !== "object") {
    // The provided value is not an object; this is an error.
    throw new TypeError(
      `${PISCĒS}: Tried to set property but provided value was not an object: ${V}`,
    );
  } else if (!deleteProperty(O, P)) {
    // The provided property could not be deleted on the provided
    // value; this is an error.
    throw new TypeError(
      `${PISCĒS}: Tried to delete property from object but [[Delete]] returned false: ${P}`,
    );
  } else {
    // The provided property was successfully deleted.
    //
    // Return the provided value.
    return O;
  }
};

/**
 * Marks the provided object as non·extensible and marks all its
 * properties as nonconfigurable and (if data properties) nonwritable,
 * and returns the object.
 *
 * ※ This is effectively an alias for `Object.freeze´.
 */
export const freeze = (O) => objectFreeze(O);

/**
 * Returns a new frozen shallow copy of the enumerable own properties
 * of the provided object, according to the following rules :—
 *
 * - For data properties, create a nonconfigurable, nonwritable
 *   property with the same value.
 *
 * - For accessor properties, create a nonconfigurable accessor
 *   property with the same getter ⹐and⹑ setter.
 *
 * The prototype for the resulting object will be taken from the
 * `.prototype´ property of the provided constructor, or the
 * `.prototype´ of the `.constructor´ of the provided object if the
 * provided constructor is undefined. If the used constructor has a
 * nonnullish `.[Symbol.species]´, that will be used instead. If the
 * used constructor or species is nullish or does not have a
 * `.prototype´ property, the prototype is set to null.
 *
 * ※ The prototype of the provided object itself is ignored.
 */
export const frozenCopy = (O, constructor = O?.constructor) => {
  if (O == null) {
    // O is null or undefined.
    throw new TypeError(
      `${PISCĒS}: Cannot copy properties of null or undefined.`,
    );
  } else {
    // O is not null or undefined.
    //
    // (If not provided, the constructor will be the value of getting
    // the `.constructor´ property of O.)
    const species = constructor?.[SPECIES] ?? constructor;
    const copy = create(
      species == null || !("prototype" in species)
        ? null
        : species.prototype,
    );
    const keys = ownKeys(O);
    for (let k = 0; k < keys.length; ++k) {
      // Iterate over each key and define the appropriate value on the
      // result.
      const P = keys[k];
      const Desc = getOwnPropertyDescriptor(O, P);
      if (Desc.enumerable) {
        // P is an enumerable property.
        defineProperty(
          copy,
          P,
          assign(
            create(null),
            isAccessorDescriptor(Desc)
              ? {
                configurable: false,
                enumerable: true,
                get: Desc.get,
                set: Desc.set,
              }
              : {
                configurable: false,
                enumerable: true,
                value: Desc.value,
                writable: false,
              },
          ),
        );
      } else {
        // P is not an enumerable property.
        /* do nothing */
      }
    }
    return objectPreventExtensions(copy);
  }
};

/**
 * Returns the function on the provided value at the provided property
 * key.
 *
 * ☡ This function throws if the provided property key does not have an
 * associated value which is either nullish or callable.
 */
export const getMethod = (V, P) => {
  const func = V[P];
  if (func == null) {
    // The value of the provided property is nullish.
    //
    // Return undefined.
    return UNDEFINED;
  } else if (typeof func !== "function") {
    // The value of the provided property is not callable; this is an
    // error.
    throw new TypeError(`${PISCĒS}: Method not callable: ${P}`);
  } else {
    // The value of the provided property is callable.
    //
    // Return it.
    return func;
  }
};

/**
 * Returns the property descriptor record for the own property with the
 * provided property key on the provided value, or null if none exists.
 *
 * ※ This is effectively an alias for
 * `Object.getOwnPropertyDescriptor´, but the return value is a proxied
 * object with null prototype.
 */
export const getOwnPropertyDescriptor = (O, P) => {
  const desc = objectGetOwnPropertyDescriptor(O, P);
  return desc === UNDEFINED
    ? UNDEFINED
    : toPropertyDescriptorRecord(desc);
};

/**
 * Returns the property descriptors for the own properties on the
 * provided value.
 *
 * ※ This is effectively an alias for
 * `Object.getOwnPropertyDescriptors´, but the values on the resulting
 * object are proxied objects with null prototypes.
 */
export const getOwnPropertyDescriptors = (O) => {
  const obj = toObject(O);
  const keys = ownKeys(obj);
  const descriptors = {};
  for (let k = 0; k < keys.length; ++k) {
    // Iterate over the keys of the provided object and collect its
    // descriptors.
    const key = keys[k];
    defineOwnDataProperty(
      descriptors,
      key,
      getOwnPropertyDescriptor(O, key),
    );
  }
  return descriptors;
};

/**
 * Returns an array of own property entries on the provided value,
 * using the provided receiver if given.
 */
export const getOwnPropertyEntries = (O, Receiver = O) => {
  const obj = toObject(O);
  const keys = ownKeys(obj);
  const target = Receiver === UNDEFINED ? obj : toObject(Receiver);
  const result = createArray(keys.length);
  for (let k = 0; k < keys.length; ++k) {
    // Iterate over each key and add the corresponding entry to the
    // result.
    const key = keys[k];
    defineOwnDataProperty(
      result,
      k,
      [key, getOwnPropertyValue(obj, keys[k], target)],
    );
  }
  return result;
};

/**
 * Returns an array of own property keys on the provided value.
 *
 * ※ This is effectively an alias for `Reflect.ownKeys´, except that
 * it does not require that the argument be an object.
 */
export const getOwnPropertyKeys = (O) => ownKeys(toObject(O));

/**
 * Returns an array of string‐valued own property keys on the
 * provided value.
 *
 * ☡ This includes both enumerable and non·enumerable properties.
 *
 * ※ This is effectively an alias for `Object.getOwnPropertyNames´.
 */
export const getOwnPropertyStrings = (O) => getOwnPropertyNames(O);

/**
 * Returns an array of symbol‐valued own property keys on the
 * provided value.
 *
 * ☡ This includes both enumerable and non·enumerable properties.
 *
 * ※ This is effectively an alias for
 * `Object.getOwnPropertySymbols´.
 */
export const getOwnPropertySymbols = (O) =>
  objectGetOwnPropertySymbols(O);

/**
 * Returns the value of the provided own property on the provided
 * value using the provided receiver, or undefined if the provided
 * property is not an own property on the provided value.
 *
 * ※ If the receiver is not provided, it defaults to the provided
 * value.
 */
export const getOwnPropertyValue = (O, P, Receiver = UNDEFINED) => {
  const obj = toObject(O);
  const desc = getOwnPropertyDescriptor(O, P);
  if (desc === UNDEFINED) {
    // The provided property is not an own property on the provided
    // value.
    //
    // Return undefined.
    return UNDEFINED;
  }
  if (isDataDescriptor(desc)) {
    // The provided property is a data property.
    //
    // Return its value.
    return desc.value;
  } else {
    // The provided property is an accessor property.
    //
    // Get its value using the appropriate receiver.
    const target = Receiver === UNDEFINED ? obj : toObject(Receiver);
    return call(desc.get, target, []);
  }
};

/**
 * Returns an array of own property values on the provided value, using
 * the provided receiver if given.
 */
export const getOwnPropertyValues = (O, Receiver = O) => {
  const obj = toObject(O);
  const keys = ownKeys(obj);
  const target = Receiver === UNDEFINED ? obj : toObject(Receiver);
  const result = createArray(keys.length);
  for (let k = 0; k < keys.length; ++k) {
    // Iterate over each key and collect the values.
    defineOwnDataProperty(
      result,
      k,
      getOwnPropertyValue(obj, keys[k], target),
    );
  }
  return result;
};

/**
 * Returns the value of the provided property key on the provided
 * value.
 *
 * ※ This is effectively an alias for `Reflect.get´, except that it
 * does not require that the argument be an object.
 */
export const getPropertyValue = (O, P, Receiver = O) =>
  get(toObject(O), P, Receiver);

/**
 * Returns the prototype of the provided value.
 *
 * ※ This is effectively an alias for `Object.getPrototypeOf´.
 */
export const getPrototype = (O) => getPrototypeOf(O);

/**
 * Returns whether the provided value has an own property with the
 * provided property key.
 *
 * ※ This is effectively an alias for `Object.hasOwn´.
 */
export const hasOwnProperty = (O, P) => hasOwn(O, P);

/**
 * Returns whether the provided property key exists on the provided
 * value.
 *
 * ※ This is effectively an alias for `Reflect.has´, except that it
 * does not require that the argument be an object.
 *
 * ※ This includes properties present on the prototype chain.
 */
export const hasProperty = (O, P) => has(toObject(O), P);

/** Returns whether the provided value is an arraylike object. */
export const isArraylikeObject = ($) => {
  if (type($) !== "object") {
    // The provided value is not an object.
    return false;
  } else {
    // The provided value is an object.
    try {
      // Try to get the length and return true.
      //
      // ※ If this throws, the object is not arraylike.
      lengthOfArraylike($);
      return true;
    } catch {
      // Getting the length failed; return false.
      return false;
    }
  }
};

/**
 * Returns whether the provided value is spreadable during array
 * concatenation.
 *
 * This is also used to determine which things should be treated as
 * collections.
 */
export const isConcatSpreadableObject = ($) => {
  if (type($) !== "object") {
    // The provided value is not an object.
    return false;
  } else {
    // The provided value is an object.
    const spreadable = $[IS_CONCAT_SPREADABLE];
    return spreadable !== UNDEFINED ? !!spreadable : isArray($);
  }
};

/**
 * Returns whether the provided value is an extensible object.
 *
 * ※ This function returns false for nonobjects.
 *
 * ※ This is effectively an alias for `Object.isExtensible´.
 */
export const isExtensibleObject = (O) => isExtensible(O);

export const {
  /**
   * Returns whether the provided value is a property descriptor record
   * as created by `toPropertyDescriptor´.
   *
   * ※ This function is provided to enable inspection of whether an
   * object uses the ♓🧩 Piscēs property descriptor record proxy
   * implementation, not as a general test of whether an object
   * satisfies the requirements for property descriptors. In most
   * cases, a more specific test, like `isAccessorDescriptor´,
   * `isDataDescriptor´, or `isGenericDescriptor´, is preferrable.
   */
  isPropertyDescriptorRecord,

  /**
   * Converts the provided value to a property descriptor record.
   *
   * ※ The prototype of a property descriptor record is always `null´.
   *
   * ※ Actually constructing a property descriptor object using this
   * class is only necessary if you need strict guarantees about the
   * types of its properties; the resulting object is proxied to ensure
   * the types match what one would expect from composing
   * `FromPropertyDescriptor´ and `ToPropertyDescriptor´ in the
   * Ecmascript specification.
   */
  toPropertyDescriptorRecord,
} = (() => {
  const proxyConstructor = Proxy;
  const { add: weakSetAdd, has: weakSetHas } = WeakSet.prototype;
  const propertyDescriptorRecords = new WeakSet();
  const coercePropertyDescriptorValue = (P, V) => {
    switch (P) {
      case "configurable":
      case "enumerable":
      case "writable":
        return !!V;
      case "value":
        return V;
      case "get":
        if (V !== UNDEFINED && typeof V !== "function") {
          // The provided value is not callable; this is an error.
          throw new TypeError(
            `${PISCĒS}: Getters must be callable.`,
          );
        } else {
          // The provided value is callable.
          return V;
        }
      case "set":
        if (V !== UNDEFINED && typeof V !== "function") {
          // The provided value is not callable; this is an error.
          throw new TypeError(
            `${PISCĒS}: Setters must be callable.`,
          );
        } else {
          // The provided value is callable.
          return V;
        }
      default:
        return V;
    }
  };
  const propertyDescriptorProxyHandler = objectFreeze(
    assign(
      create(null),
      {
        defineProperty(O, P, Desc) {
          if (
            P === "configurable" || P === "enumerable"
            || P === "writable" || P === "value"
            || P === "get" || P === "set"
          ) {
            // `P´ is a property descriptor attribute.
            const desc = assign(objectCreate(null), Desc);
            if ("get" in desc || "set" in desc) {
              // `Desc´ is an accessor property descriptor.
              throw new TypeError(
                `${PISCĒS}: Property descriptor attributes must be data properties.`,
              );
            } else if ("value" in desc || !(P in O)) {
              // `Desc´ has a value or `P´ does not already exist on
              // `O´.
              desc.value = coercePropertyDescriptorValue(
                P,
                desc.value,
              );
            } else {
              // `Desc´ is not an accessor property descriptor and has
              // no value, but an existing value is present on `O´.
              /* do nothing */
            }
            const isAccessorDescriptor = "get" === P || "set" === P
              || "get" in O || "set" in O;
            const isDataDescriptor = "value" === P
              || "writable" === P
              || "value" in O || "writable" in O;
            if (isAccessorDescriptor && isDataDescriptor) {
              // Both accessor and data attributes will be present on
              // `O´ after defining `P´; this is an error.
              throw new TypeError(
                `${PISCĒS}: Property descriptors cannot specify both accessor and data attributes.`,
              );
            } else {
              // `P´ can be safely defined on `O´.
              return reflectDefineProperty(O, P, desc);
            }
          } else {
            // `P´ is not a property descriptor attribute.
            return reflectDefineProperty(O, P, Desc);
          }
        },
        setPrototypeOf(O, V) {
          if (V !== null) {
            // `V´ is not the property descriptor prototype.
            return false;
          } else {
            // `V´ is the property descriptor prototype.
            return reflectSetPrototypeOf(O, V);
          }
        },
      },
    ),
  );

  return {
    isPropertyDescriptorRecord: ($) =>
      call(weakSetHas, propertyDescriptorRecords, [$]),
    toPropertyDescriptorRecord: (Obj) => {
      if (type(Obj) !== "object") {
        // The provided value is not an object; this is an error.
        throw new TypeError(
          `${PISCĒS}: Cannot convert primitive to property descriptor: ${O}.`,
        );
      } else {
        // The provided value is an object.
        const desc = create(null);
        if ("enumerable" in Obj) {
          // An enumerable property is specified.
          defineOwnDataProperty(desc, "enumerable", !!Obj.enumerable);
        } else {
          // An enumerable property is not specified.
          /* do nothing */
        }
        if ("configurable" in Obj) {
          // A configurable property is specified.
          defineOwnDataProperty(
            desc,
            "configurable",
            !!Obj.configurable,
          );
        } else {
          // A configurable property is not specified.
          /* do nothing */
        }
        if ("value" in Obj) {
          // A value property is specified.
          defineOwnDataProperty(desc, "value", Obj.value);
        } else {
          // A value property is not specified.
          /* do nothing */
        }
        if ("writable" in Obj) {
          // A writable property is specified.
          defineOwnDataProperty(desc, "writable", !!Obj.writable);
        } else {
          // A writable property is not specified.
          /* do nothing */
        }
        if ("get" in Obj) {
          // A get property is specified.
          const getter = Obj.get;
          if (getter !== UNDEFINED && typeof getter !== "function") {
            // The getter is not callable; this is an error.
            throw new TypeError(
              `${PISCĒS}: Getters must be callable.`,
            );
          } else {
            // The getter is callable.
            defineOwnDataProperty(desc, "get", Obj.get);
          }
        } else {
          // A get property is not specified.
          /* do nothing */
        }
        if ("set" in Obj) {
          // A set property is specified.
          const setter = Obj.set;
          if (setter !== UNDEFINED && typeof setter !== "function") {
            // The setter is not callable; this is an error.
            throw new TypeError(
              `${PISCĒS}: Setters must be callable.`,
            );
          } else {
            // The setter is callable.
            defineOwnDataProperty(desc, "set", Obj.set);
          }
        } else {
          // A set property is not specified.
          /* do nothing */
        }
        if (
          ("get" in desc || "set" in desc)
          && ("value" in desc || "writable" in desc)
        ) {
          // Both accessor and data attributes have been defined; this
          // is an error.
          throw new TypeError(
            `${PISCĒS}: Property descriptors cannot specify both accessor and data attributes.`,
          );
        } else {
          // The property descriptor is valid.
          const record = new proxyConstructor(
            desc,
            propertyDescriptorProxyHandler,
          );
          call(weakSetAdd, propertyDescriptorRecords, [record]);
          return record;
        }
      }
    },
  };
})();

/**
 * Returns whether the provided value is an unfrozen object.
 *
 * ※ This function returns false for nonobjects.
 *
 * ※ This is effectively an alias for `!Object.isFrozen´.
 */
export const isUnfrozenObject = (O) => !isFrozen(O);

/**
 * Returns whether the provided value is an unsealed object.
 *
 * ※ This function returns false for nonobjects.
 *
 * ※ This is effectively an alias for `!Object.isSealed´.
 */
export const isUnsealedObject = (O) => !isSealed(O);

/**
 * Returns the length of the provided arraylike value.
 *
 * This can produce larger lengths than can actually be stored in
 * arrays, because no such restrictions exist on arraylike methods.
 *
 * ☡ This function throws if the provided value is not arraylike.
 */
export const lengthOfArraylike = ({ length }) => toLength(length);

/**
 * Returns an array of key~value pairs for the enumerable,
 * string‐valued property keys on the provided value.
 *
 * ※ This is effectively an alias for `Object.entries´.
 */
export const namedEntries = (O) => entries(O);

/**
 * Returns an array of the enumerable, string‐valued property keys on
 * the provided value.
 *
 * ※ This is effectively an alias for `Object.keys´.
 */
export const namedKeys = (O) => keys(O);

/**
 * Returns an array of property values for the enumerable,
 * string‐valued property keys on the provided value.
 *
 * ※ This is effectively an alias for `Object.values´.
 */
export const namedValues = (O) => values(O);

/**
 * Returns a new object with the provided prototype and property
 * descriptors.
 *
 * ※ This is effectively an alias for `Object.create´.
 */
export const objectCreate = (O, Properties) => create(O, Properties);

/**
 * Returns a new object with property keys and values from the provided
 * iterable value.
 *
 * ※ This is effectively an alias for `Object.fromEntries´.
 */
export const objectFromEntries = (iterable) => fromEntries(iterable);

/**
 * Marks the provided object as non·extensible, and returns the
 * object.
 *
 * ※ This is effectively an alias for `Object.preventExtensions´.
 */
export const preventExtensions = (O) => objectPreventExtensions(O);

/**
 * Marks the provided object as non·extensible and marks all its
 * properties as nonconfigurable, and returns the object.
 *
 * ※ This is effectively an alias for `Object.seal´.
 */
export const seal = (O) => objectSeal(O);

/**
 * Sets the provided property key to the provided value on the provided
 * object and returns the object.
 *
 * ※ This function differs from `Reflect.set´ in that it throws if the
 * setting is unsuccessful.
 *
 * ☡ This function throws if the first argument is not an object.
 */
export const setPropertyValue = (O, P, V, Receiver = O) => {
  if (type(O) !== "object") {
    // The provided value is not an object; this is an error.
    throw new TypeError(
      `${PISCĒS}: Tried to set property but provided value was not an object: ${V}`,
    );
  } else if (!set(O, P, V, Receiver)) {
    // Setting the property fails; this is an error.
    throw new TypeError(
      `${PISCĒS}: Tried to set property on object but [[Set]] returned false: ${P}`,
    );
  } else {
    // The property was successfully set.
    //
    // Return the provided object.
    return O;
  }
};

/**
 * Sets the values of the enumerable own properties of the provided
 * additional objects on the provided values.
 *
 * ※ This is effectively an alias for `Object.assign´.
 */
export const setPropertyValues = (target, source, ...sources) => {
  const to = toObject(target);
  for (let i = -1; i < sources.length; ++i) {
    // Iterate over each source and set the appropriate property
    // values.
    const nextSource = i === -1 ? source : sources[i];
    if (nextSource != null) {
      // The current source is not nullish.
      //
      // Handle its own properties.
      const from = toObject(nextSource);
      const keys = ownKeys(from);
      for (let k = 0; k < keys.length; ++k) {
        // Iterate over each key in the current source and set it in
        // the target object if it is enumerable.
        const nextKey = keys[k];
        const desc = reflectGetOwnPropertyDescriptor(from, nextKey);
        if (desc !== UNDEFINED && desc.enumerable) {
          // The current key is present and enumerable.
          //
          // Set it to its corresponding value.
          const propValue = from[nextKey];
          to[nextKey] = propValue;
        } else {
          // The current key is not present or not enumerable.
          /* do nothing */
        }
      }
    } else {
      // The current source is nullish.
      /* do nothing */
    }
  }
  return to;
};

/**
 * Sets the prototype of the provided object to the provided value and
 * returns the object.
 *
 * ※ This is effectively an alias for `Object.setPrototypeOf´, but it
 * won¦t throw when setting the prototype of a primitive to its current
 * value.
 */
export const setPrototype = (O, proto) => {
  const obj = toObject(O);
  if (O === obj) {
    // The provided value is an object.
    //
    // Set its prototype normally.
    return setPrototypeOf(O, proto);
  } else {
    // The provided value is not an object.
    //
    // Attempt to set the prototype on a coerced version with
    // extensions prevented, then return the provided value.
    //
    // ☡ This will throw if the given prototype does not match the
    // existing one on the coerced object.
    setPrototypeOf(objectPreventExtensions(obj), proto);
    return O;
  }
};

/**
 * Returns the provided value converted to an object.
 *
 * Existing objects are returned with no modification.
 *
 * ☡ This function throws if its argument is null or undefined.
 */
export const toObject = ($) => {
  if ($ == null) {
    // The provided value is nullish; this is an error.
    throw new TypeError(
      `${PISCĒS}: Cannot convert ${$} into an object.`,
    );
  } else {
    // The provided value is not nullish.
    //
    // Coerce it to an object.
    return object($);
  }
};