feat: use iterable object directly

[LviatYi]

BackGround

In C#, iterable objects can be iterated over using LINQ in the following way:

var list = users
  .Where(u => user.Name.Contains("Yi"))
  .Select(u => u.id);

Here, users is an object of type IEnumerable<T>, meaning it implements the IEnumerator interface.

IEnumerable | MSDN

In JS/Ts, a similar concept exists for iterables.
For example, Map is an iterable object that can be iterated by for...of because it implements the Iterable<T> interface (Ts), i.e., it contains a [Symbol.iterator] method.

Feature

This pull request enhances the from function by enabling it to accept Iterable<T> objects.

This PR aims to automatically invoke the [Symbol.iterator] method on objects that possess it to obtain an iterator, and then use this iterator to construct an Enumerable.

Key Changes

• New:

    // Enumerable.from
    {
        // iterable object
        if (typeof Symbol !== 'undefined' && typeof obj[Symbol.iterator] !== 'undefined') {
            let iterator;
            return new Enumerable(function () {
                return new IEnumerator(
                    function () {
                        iterator = obj[Symbol.iterator]()
                    },
                    function () {
                        var next = iterator.next();
                        return (next.done ? false : (this.yieldReturn(next.value)));
                    },
                    Functions.Blank);
            });
        }
    }

  • check if obj has a [Symbol.iterator] method. if ture, treat it as an iterable object.

Why

• More Direct Usage: This change will accept iterable objects directly. For instance:

    const map = new Map();
  
    map.set(1, 2);
    map.set(2, 4);
  
    let result = Enumerable.from(map)
        .select(item => ({key: item[0], value: item[1]}))
        .select(item => item.key)
        .toArray();
  
    console.log(result);

  The above code will throw an error in 4.0.2 version because map is an iterable object, but linq treats it as an iterator and accesses its next function directly:

  Uncaught TypeError: obj.next is not a function
  

  In PR#110, an empty array is provided. The reason is that PR#110 expects an iterator rather than an iterable object. The following code will return the expected results:

    Enumerable.from(map[Symbol.iterator]())

This PR is more dangerous than last time. The last PR actually targeted a function signature that was not correctly aligned with linq.d.ts and corrected it to be fully compliant.
This PR adds a new feature, enabling the Enumerable.from function to accept parameters of type Iterable<T>. This is a completely new feature and may introduce new problems.

Thank you very much to the author for pointing out the problem of modifying irrelevant code. I will try to avoid this behavior in subsequent PRs.

This PR also reverts iterator.js:14-22 with changes from an unrelated commit.

[mihaifm]

Thanks. I released a new version with your fixes.