Introduction
I am currently work in project that I need to save the score of each user.
For this I used a Map<User, number> to represent it.
Problematic
If I create map with a user named john:
let myMap: Map<User, number> = new Map();
myMap.set(new User("John","Hasherman"), 0);
And if I want to set John Hasherman’s score to 1 (voluntarily using a new instance and not the one previously used), with this code:
myMap.set(new User("John","Hasherman"), 1);
But TypeScript create a new element inside myMap.
Question
So my question is, do you know if it’s possible to customize the comparator used inside the map? like Java when defining hashCode() and equals(o Object)?
You'll need a way for the User to expose functionality that will identify a particular user, perhaps by name, or perhaps by a more unique ID. Either way, a Map where each user is the key isn't very suited to the job, but it's possible.
class User {
public first: string;
public last: string;
constructor(first: string, last: string) {
this.first = first;
this.last = last;
}
}
const myMap: Map<User, number> = new Map();
myMap.set(new User("John","Hasherman"), 0);
// to set John's value to 1:
const foundJohn = [...myMap.keys()].find(
obj => obj.first === 'John' && obj.last === 'Hasherman'
);
if (foundJohn) {
myMap.set(foundJohn, 1);
}
It's somewhat convoluted. I'd suggest considering a different data structure if possible.
Related
New ES 6 (Harmony) introduces new Set object. Identity algorithm used by Set is similar to === operator and so not much suitable for comparing objects:
var set = new Set();
set.add({a:1});
set.add({a:1});
console.log([...set.values()]); // Array [ Object, Object ]
How to customize equality for Set objects in order to do deep object comparison? Is there anything like Java equals(Object)?
Update 3/2022
There is currently a proposal to add Records and Tuples (basically immutable Objects and Arrays) to Javascript. In that proposal, it offers direct comparison of Records and Tuples using === or !== where it compares values, not just object references AND relevant to this answer both Set and Map objects would use the value of the Record or Tuple in key comparisons/lookups which would solve what is being asked for here.
Since the Records and Tuples are immutable (can't be modified) and because they are easily compared by value (by their contents, not just their object reference), it allows Maps and Sets to use object contents as keys and the proposed spec explicitly names this feature for Sets and Maps.
This original question asked for customizability of a Set comparison in order to support deep object comparison. This doesn't propose customizability of the Set comparison, but it directly supports deep object comparison if you use the new Record or a Tuple instead of an Object or an Array and thus would solve the original problem here.
Note, this proposal advanced to Stage 2 in mid-2021. It has been moving forward recently, but is certainly not done.
Mozilla work on this new proposal can be tracked here.
Original Answer
The ES6 Set object does not have any compare methods or custom compare extensibility.
The .has(), .add() and .delete() methods work only off it being the same actual object or same value for a primitive and don't have a means to plug into or replace just that logic.
You could presumably derive your own object from a Set and replace .has(), .add() and .delete() methods with something that did a deep object comparison first to find if the item is already in the Set, but the performance would likely not be good since the underlying Set object would not be helping at all. You'd probably have to just do a brute force iteration through all existing objects to find a match using your own custom compare before calling the original .add().
Here's some info from this article and discussion of ES6 features:
5.2 Why can’t I configure how maps and sets compare keys and values?
Question: It would be nice if there were a way to configure what map
keys and what set elements are considered equal. Why isn’t there?
Answer: That feature has been postponed, as it is difficult to
implement properly and efficiently. One option is to hand callbacks to
collections that specify equality.
Another option, available in Java, is to specify equality via a method
that object implement (equals() in Java). However, this approach is
problematic for mutable objects: In general, if an object changes, its
“location” inside a collection has to change, as well. But that’s not
what happens in Java. JavaScript will probably go the safer route of
only enabling comparison by value for special immutable objects
(so-called value objects). Comparison by value means that two values
are considered equal if their contents are equal. Primitive values are
compared by value in JavaScript.
As mentioned in jfriend00's answer customization of equality relation is probably not possible.
Following code presents an outline of computationally efficient (but memory expensive) workaround:
class GeneralSet {
constructor() {
this.map = new Map();
this[Symbol.iterator] = this.values;
}
add(item) {
this.map.set(item.toIdString(), item);
}
values() {
return this.map.values();
}
delete(item) {
return this.map.delete(item.toIdString());
}
// ...
}
Each inserted element has to implement toIdString() method that returns string. Two objects are considered equal if and only if their toIdString methods returns same value.
As the top answer mentions, customizing equality is problematic for mutable objects. The good news is (and I'm surprised no one has mentioned this yet) there's a very popular library called immutable-js that provides a rich set of immutable types which provide the deep value equality semantics you're looking for.
Here's your example using immutable-js:
const { Map, Set } = require('immutable');
var set = new Set();
set = set.add(Map({a:1}));
set = set.add(Map({a:1}));
console.log([...set.values()]); // [Map {"a" => 1}]
Maybe you can try to use JSON.stringify() to do deep object comparison.
for example :
const arr = [
{name:'a', value:10},
{name:'a', value:20},
{name:'a', value:20},
{name:'b', value:30},
{name:'b', value:40},
{name:'b', value:40}
];
const names = new Set();
const result = arr.filter(item => !names.has(JSON.stringify(item)) ? names.add(JSON.stringify(item)) : false);
console.log(result);
To add to the answers here, I went ahead and implemented a Map wrapper that takes a custom hash function, a custom equality function, and stores distinct values that have equivalent (custom) hashes in buckets.
Predictably, it turned out to be slower than czerny's string concatenation method.
Full source here: https://github.com/makoConstruct/ValueMap
Comparing them directly seems not possible, but JSON.stringify works if the keys just were sorted. As I pointed out in a comment
JSON.stringify({a:1, b:2}) !== JSON.stringify({b:2, a:1});
But we can work around that with a custom stringify method. First we write the method
Custom Stringify
Object.prototype.stringifySorted = function(){
let oldObj = this;
let obj = (oldObj.length || oldObj.length === 0) ? [] : {};
for (let key of Object.keys(this).sort((a, b) => a.localeCompare(b))) {
let type = typeof (oldObj[key])
if (type === 'object') {
obj[key] = oldObj[key].stringifySorted();
} else {
obj[key] = oldObj[key];
}
}
return JSON.stringify(obj);
}
The Set
Now we use a Set. But we use a Set of Strings instead of objects
let set = new Set()
set.add({a:1, b:2}.stringifySorted());
set.has({b:2, a:1}.stringifySorted());
// returns true
Get all the values
After we created the set and added the values, we can get all values by
let iterator = set.values();
let done = false;
while (!done) {
let val = iterator.next();
if (!done) {
console.log(val.value);
}
done = val.done;
}
Here's a link with all in one file
http://tpcg.io/FnJg2i
For Typescript users the answers by others (especially czerny) can be generalized to a nice type-safe and reusable base class:
/**
* Map that stringifies the key objects in order to leverage
* the javascript native Map and preserve key uniqueness.
*/
abstract class StringifyingMap<K, V> {
private map = new Map<string, V>();
private keyMap = new Map<string, K>();
has(key: K): boolean {
let keyString = this.stringifyKey(key);
return this.map.has(keyString);
}
get(key: K): V {
let keyString = this.stringifyKey(key);
return this.map.get(keyString);
}
set(key: K, value: V): StringifyingMap<K, V> {
let keyString = this.stringifyKey(key);
this.map.set(keyString, value);
this.keyMap.set(keyString, key);
return this;
}
/**
* Puts new key/value if key is absent.
* #param key key
* #param defaultValue default value factory
*/
putIfAbsent(key: K, defaultValue: () => V): boolean {
if (!this.has(key)) {
let value = defaultValue();
this.set(key, value);
return true;
}
return false;
}
keys(): IterableIterator<K> {
return this.keyMap.values();
}
keyList(): K[] {
return [...this.keys()];
}
delete(key: K): boolean {
let keyString = this.stringifyKey(key);
let flag = this.map.delete(keyString);
this.keyMap.delete(keyString);
return flag;
}
clear(): void {
this.map.clear();
this.keyMap.clear();
}
size(): number {
return this.map.size;
}
/**
* Turns the `key` object to a primitive `string` for the underlying `Map`
* #param key key to be stringified
*/
protected abstract stringifyKey(key: K): string;
}
Example implementation is then this simple: just override the stringifyKey method. In my case I stringify some uri property.
class MyMap extends StringifyingMap<MyKey, MyValue> {
protected stringifyKey(key: MyKey): string {
return key.uri.toString();
}
}
Example usage is then as if this was a regular Map<K, V>.
const key1 = new MyKey(1);
const value1 = new MyValue(1);
const value2 = new MyValue(2);
const myMap = new MyMap();
myMap.set(key1, value1);
myMap.set(key1, value2); // native Map would put another key/value pair
myMap.size(); // returns 1, not 2
A good stringification method for the special but frequent case of a TypedArray as Set/Map key is using
const key = String.fromCharCode(...new Uint16Array(myArray.buffer));
It generates the shortest possible unique string that can be easily converted back. However this is not always a valid UTF-16 string for display concerning Low and High Surrogates. Set and Map seem to ignore surrogate validity.
As measured in Firefox and Chrome, the spread operator performs slowly. If your myArray has fixed size, it executes faster when you write:
const a = new Uint16Array(myArray.buffer); // here: myArray = Uint32Array(2) = 8 bytes
const key = String.fromCharCode(a[0],a[1],a[2],a[3]); // 8 bytes too
Probably the most valuable advantage of this method of key-building: It works for Float32Array and Float64Array without any rounding side-effect. Note that +0 and -0 are then different. Infinities are same. Silent NaNs are same. Signaling NaNs are different depending on their signal (never seen in vanilla JavaScript).
As other guys said there is no native method can do it by far.
But if you would like to distinguish an array with your custom comparator, you can try to do it with the reduce method.
function distinct(array, equal) {
// No need to convert it to a Set object since it may give you a wrong signal that the set can work with your objects.
return array.reduce((p, c) => {
p.findIndex((element) => equal(element, c)) > -1 || p.push(c);
return p;
}, []);
}
// You can call this method like below,
const users = distinct(
[
{id: 1, name: "kevin"},
{id: 2, name: "sean"},
{id: 1, name: "jerry"}
],
(a, b) => a.id === b.id
);
...
As others have said, there is no way to do it with the current version of Set.
My suggestion is to do it using a combination of arrays and maps.
The code snipped below will create a map of unique keys based on your own defined key and then transform that map of unique items into an array.
const array =
[
{ "name": "Joe", "age": 17 },
{ "name": "Bob", "age": 17 },
{ "name": "Carl", "age": 35 }
]
const key = 'age';
const arrayUniqueByKey = [...new Map(array.map(item =>
[item[key], item])).values()];
console.log(arrayUniqueByKey);
/*OUTPUT
[
{ "name": "Bob", "age": 17 },
{ "name": "Carl", "age": 35 }
]
*/
// Note: this will pick the last duplicated item in the list.
To someone who found this question on Google (as me) wanting to get a value of a Map using an object as Key:
Warning: this answer will not work with all objects
var map = new Map<string,string>();
map.set(JSON.stringify({"A":2} /*string of object as key*/), "Worked");
console.log(map.get(JSON.stringify({"A":2}))||"Not worked");
Output:
Worked
In javascript there is an easy way to generate cloned object with some of the fields updated:
const person = {
isHuman: false,
name: "gabe"
};
const person2 = {
...person1,
name: 'alice'
}
Is there a way to do something like in groovy without copying all the fields manually? I am writing testcases where I wanna generate data with one attribute changed at a time.
Can you use #Immutable(copyWith = true)
#Immutable(copyWith = true)
class Person {
String first, last
}
def tim = new Person('tim', 'yates')
def alice = tim.copyWith(first:'alice')
assert tim.first == 'tim'
assert alice.first == 'alice'
https://docs.groovy-lang.org/latest/html/gapi/groovy/transform/ImmutableBase.html#copyWith
There are many ways this can be done.
One is to construct instances by spreading in a map, e.g., given:
class Person { String name; Boolean isHuman; }
An instance can be constructed using the same spread-map operator I linked to:
m1 = [ name: "Gabe", isHuman: true ]
p1 = new Person(*:m1)
println p1
// Person: Gabe, isHuman=true
This avoids actual work. An exception will be thrown if a map key isn't an instance property.
A utility method grabbing (non-synthetic) prop names from a class, and iterates while putting the name/value pairs into a map is also an option (and affords a bit more safety):
def toMap(obj) {
obj.class.declaredFields
.findAll { !it.synthetic }
.collectEntries { [(it.name): obj."$it.name" ] }
}
Now we can construct a "prototype" object, but override properties:
p2 = new Person(*:toMap(p1), name: "Alice")
println p2
// Person: Alice, isHuman=true
There are also libraries that do this type of work.
Depending on your actual usecase it may not be necessary to do anything other than passing a map, however (duck typing).
I'm working on re-engineering this persons code:
https://stackblitz.com/edit/angular-sx79hu?embed=1&file=app/multiselect-autocomplete-example.html
So i have a User class:
export class User {
constructor(public code: string, public description: string, public selected: boolean ) {
if (selected === undefined) selected = false;
}
}
and I have another array (NewArray) that I am going to receive via service. It will be an array of objects with 'i' number of elements, each object with props {"prop1":"value1", "prop2":"value2"}
I'm trying to create a new Array called Users which will use the User class like so BUT will get the elements by looping through NewArray:
users = [new User('i.prop1','i.prop2', false)]
but I only get the last index instead of all from 0 to i.
What am I missing here? Thanks!
you need to use something like below. Check and let me know if it works.
users = [];
newArray.forEach((item, i) => {
users.push(new User( item.prop1, item.prop2, false));
}):
New ES 6 (Harmony) introduces new Set object. Identity algorithm used by Set is similar to === operator and so not much suitable for comparing objects:
var set = new Set();
set.add({a:1});
set.add({a:1});
console.log([...set.values()]); // Array [ Object, Object ]
How to customize equality for Set objects in order to do deep object comparison? Is there anything like Java equals(Object)?
Update 3/2022
There is currently a proposal to add Records and Tuples (basically immutable Objects and Arrays) to Javascript. In that proposal, it offers direct comparison of Records and Tuples using === or !== where it compares values, not just object references AND relevant to this answer both Set and Map objects would use the value of the Record or Tuple in key comparisons/lookups which would solve what is being asked for here.
Since the Records and Tuples are immutable (can't be modified) and because they are easily compared by value (by their contents, not just their object reference), it allows Maps and Sets to use object contents as keys and the proposed spec explicitly names this feature for Sets and Maps.
This original question asked for customizability of a Set comparison in order to support deep object comparison. This doesn't propose customizability of the Set comparison, but it directly supports deep object comparison if you use the new Record or a Tuple instead of an Object or an Array and thus would solve the original problem here.
Note, this proposal advanced to Stage 2 in mid-2021. It has been moving forward recently, but is certainly not done.
Mozilla work on this new proposal can be tracked here.
Original Answer
The ES6 Set object does not have any compare methods or custom compare extensibility.
The .has(), .add() and .delete() methods work only off it being the same actual object or same value for a primitive and don't have a means to plug into or replace just that logic.
You could presumably derive your own object from a Set and replace .has(), .add() and .delete() methods with something that did a deep object comparison first to find if the item is already in the Set, but the performance would likely not be good since the underlying Set object would not be helping at all. You'd probably have to just do a brute force iteration through all existing objects to find a match using your own custom compare before calling the original .add().
Here's some info from this article and discussion of ES6 features:
5.2 Why can’t I configure how maps and sets compare keys and values?
Question: It would be nice if there were a way to configure what map
keys and what set elements are considered equal. Why isn’t there?
Answer: That feature has been postponed, as it is difficult to
implement properly and efficiently. One option is to hand callbacks to
collections that specify equality.
Another option, available in Java, is to specify equality via a method
that object implement (equals() in Java). However, this approach is
problematic for mutable objects: In general, if an object changes, its
“location” inside a collection has to change, as well. But that’s not
what happens in Java. JavaScript will probably go the safer route of
only enabling comparison by value for special immutable objects
(so-called value objects). Comparison by value means that two values
are considered equal if their contents are equal. Primitive values are
compared by value in JavaScript.
As mentioned in jfriend00's answer customization of equality relation is probably not possible.
Following code presents an outline of computationally efficient (but memory expensive) workaround:
class GeneralSet {
constructor() {
this.map = new Map();
this[Symbol.iterator] = this.values;
}
add(item) {
this.map.set(item.toIdString(), item);
}
values() {
return this.map.values();
}
delete(item) {
return this.map.delete(item.toIdString());
}
// ...
}
Each inserted element has to implement toIdString() method that returns string. Two objects are considered equal if and only if their toIdString methods returns same value.
As the top answer mentions, customizing equality is problematic for mutable objects. The good news is (and I'm surprised no one has mentioned this yet) there's a very popular library called immutable-js that provides a rich set of immutable types which provide the deep value equality semantics you're looking for.
Here's your example using immutable-js:
const { Map, Set } = require('immutable');
var set = new Set();
set = set.add(Map({a:1}));
set = set.add(Map({a:1}));
console.log([...set.values()]); // [Map {"a" => 1}]
Maybe you can try to use JSON.stringify() to do deep object comparison.
for example :
const arr = [
{name:'a', value:10},
{name:'a', value:20},
{name:'a', value:20},
{name:'b', value:30},
{name:'b', value:40},
{name:'b', value:40}
];
const names = new Set();
const result = arr.filter(item => !names.has(JSON.stringify(item)) ? names.add(JSON.stringify(item)) : false);
console.log(result);
To add to the answers here, I went ahead and implemented a Map wrapper that takes a custom hash function, a custom equality function, and stores distinct values that have equivalent (custom) hashes in buckets.
Predictably, it turned out to be slower than czerny's string concatenation method.
Full source here: https://github.com/makoConstruct/ValueMap
Comparing them directly seems not possible, but JSON.stringify works if the keys just were sorted. As I pointed out in a comment
JSON.stringify({a:1, b:2}) !== JSON.stringify({b:2, a:1});
But we can work around that with a custom stringify method. First we write the method
Custom Stringify
Object.prototype.stringifySorted = function(){
let oldObj = this;
let obj = (oldObj.length || oldObj.length === 0) ? [] : {};
for (let key of Object.keys(this).sort((a, b) => a.localeCompare(b))) {
let type = typeof (oldObj[key])
if (type === 'object') {
obj[key] = oldObj[key].stringifySorted();
} else {
obj[key] = oldObj[key];
}
}
return JSON.stringify(obj);
}
The Set
Now we use a Set. But we use a Set of Strings instead of objects
let set = new Set()
set.add({a:1, b:2}.stringifySorted());
set.has({b:2, a:1}.stringifySorted());
// returns true
Get all the values
After we created the set and added the values, we can get all values by
let iterator = set.values();
let done = false;
while (!done) {
let val = iterator.next();
if (!done) {
console.log(val.value);
}
done = val.done;
}
Here's a link with all in one file
http://tpcg.io/FnJg2i
For Typescript users the answers by others (especially czerny) can be generalized to a nice type-safe and reusable base class:
/**
* Map that stringifies the key objects in order to leverage
* the javascript native Map and preserve key uniqueness.
*/
abstract class StringifyingMap<K, V> {
private map = new Map<string, V>();
private keyMap = new Map<string, K>();
has(key: K): boolean {
let keyString = this.stringifyKey(key);
return this.map.has(keyString);
}
get(key: K): V {
let keyString = this.stringifyKey(key);
return this.map.get(keyString);
}
set(key: K, value: V): StringifyingMap<K, V> {
let keyString = this.stringifyKey(key);
this.map.set(keyString, value);
this.keyMap.set(keyString, key);
return this;
}
/**
* Puts new key/value if key is absent.
* #param key key
* #param defaultValue default value factory
*/
putIfAbsent(key: K, defaultValue: () => V): boolean {
if (!this.has(key)) {
let value = defaultValue();
this.set(key, value);
return true;
}
return false;
}
keys(): IterableIterator<K> {
return this.keyMap.values();
}
keyList(): K[] {
return [...this.keys()];
}
delete(key: K): boolean {
let keyString = this.stringifyKey(key);
let flag = this.map.delete(keyString);
this.keyMap.delete(keyString);
return flag;
}
clear(): void {
this.map.clear();
this.keyMap.clear();
}
size(): number {
return this.map.size;
}
/**
* Turns the `key` object to a primitive `string` for the underlying `Map`
* #param key key to be stringified
*/
protected abstract stringifyKey(key: K): string;
}
Example implementation is then this simple: just override the stringifyKey method. In my case I stringify some uri property.
class MyMap extends StringifyingMap<MyKey, MyValue> {
protected stringifyKey(key: MyKey): string {
return key.uri.toString();
}
}
Example usage is then as if this was a regular Map<K, V>.
const key1 = new MyKey(1);
const value1 = new MyValue(1);
const value2 = new MyValue(2);
const myMap = new MyMap();
myMap.set(key1, value1);
myMap.set(key1, value2); // native Map would put another key/value pair
myMap.size(); // returns 1, not 2
A good stringification method for the special but frequent case of a TypedArray as Set/Map key is using
const key = String.fromCharCode(...new Uint16Array(myArray.buffer));
It generates the shortest possible unique string that can be easily converted back. However this is not always a valid UTF-16 string for display concerning Low and High Surrogates. Set and Map seem to ignore surrogate validity.
As measured in Firefox and Chrome, the spread operator performs slowly. If your myArray has fixed size, it executes faster when you write:
const a = new Uint16Array(myArray.buffer); // here: myArray = Uint32Array(2) = 8 bytes
const key = String.fromCharCode(a[0],a[1],a[2],a[3]); // 8 bytes too
Probably the most valuable advantage of this method of key-building: It works for Float32Array and Float64Array without any rounding side-effect. Note that +0 and -0 are then different. Infinities are same. Silent NaNs are same. Signaling NaNs are different depending on their signal (never seen in vanilla JavaScript).
As other guys said there is no native method can do it by far.
But if you would like to distinguish an array with your custom comparator, you can try to do it with the reduce method.
function distinct(array, equal) {
// No need to convert it to a Set object since it may give you a wrong signal that the set can work with your objects.
return array.reduce((p, c) => {
p.findIndex((element) => equal(element, c)) > -1 || p.push(c);
return p;
}, []);
}
// You can call this method like below,
const users = distinct(
[
{id: 1, name: "kevin"},
{id: 2, name: "sean"},
{id: 1, name: "jerry"}
],
(a, b) => a.id === b.id
);
...
As others have said, there is no way to do it with the current version of Set.
My suggestion is to do it using a combination of arrays and maps.
The code snipped below will create a map of unique keys based on your own defined key and then transform that map of unique items into an array.
const array =
[
{ "name": "Joe", "age": 17 },
{ "name": "Bob", "age": 17 },
{ "name": "Carl", "age": 35 }
]
const key = 'age';
const arrayUniqueByKey = [...new Map(array.map(item =>
[item[key], item])).values()];
console.log(arrayUniqueByKey);
/*OUTPUT
[
{ "name": "Bob", "age": 17 },
{ "name": "Carl", "age": 35 }
]
*/
// Note: this will pick the last duplicated item in the list.
To someone who found this question on Google (as me) wanting to get a value of a Map using an object as Key:
Warning: this answer will not work with all objects
var map = new Map<string,string>();
map.set(JSON.stringify({"A":2} /*string of object as key*/), "Worked");
console.log(map.get(JSON.stringify({"A":2}))||"Not worked");
Output:
Worked
How to fix an error in this case (keeping using class as type):
/* #flow */
class Person {
name: string;
age: number;
}
const person: Person = new Person();
person.name = 'Bob';
person.age = 25;
['name', 'age'].forEach(key => {
if(person[key]) {
console.log(person[key]);
}
});
The error points to person[key] and says:
Cannot get person[key] because an indexer property is missing in
Person
In similar situation (may be different flow version) it says:
computed property. Indexable signature not found in Person
I think the bigger issue is that Array.prototype.forEach has the type
forEach(callbackfn: (value: T, index: number, array: $ReadOnlyArray<T>) => any, thisArg?: any): void;
https://github.com/facebook/flow/blob/3baafb0f2191353cd896d6fe087aea535bc8606e/lib/core.js#L211.
You can see that the value parameter has type T, which is determined by the type of the elements in the array. In your case, Flow is (most likely) assuming the type of the array ['name', 'age'] to be string[]. Thus, the type T is set to string.
Now, when you try to access person[key], Flow will complain that you are missing an indexer property. This is accurate since you are trying to use a generic string access on the Person instance. This problem persists even after removing the conditional, which hints that Flow is unable to refine the string type to be one of 'name' and 'age'.
It would be nice if Flow could refine something like this
/* #flow */
class Person {
name: string;
age: number;
}
const person: Person = new Person();
person.name = 'Bob';
person.age = 25;
['name', 'age'].forEach(key => {
if (key === 'name') {
console.log(person[key]);
}
});
not necessarily because it's useful but because it is so explicit and should be a safe access at that point.
I would try to avoid using a loop through a list of properties to get/set properties on an object since Flow doesn't deal with the nuances of arrays that act like tuples yet. Plus, it's more future-proof to loop through the object itself (e.g., Object.keys) in case the object's properties ever get changed.