C# keyword 'empty' compiles to the static Empty property of List, Dictionary, etc.

[JustinMinnaar]

Typically, when a function generates a list, instead of returning a NULL, it has been proposed as a best-practice to return a static empty list, preventing memory use for the creation of a new empty list, and allowing the caller to interate the list without concern about NULL. Perhaps a new keyword 'empty' could return the static property of the class with the name 'Empty'. As a convention, this may make this process easier to read.

public List<Person> GetPeople(PeopleFilter filter)
{
    if (someCondition)
        return new List<Person>();

    ...
}

This could be changed to

public List<Person> GetPeople(PeopleFilter filter)
{
    if (someCondition)
        return empty;

    ...
}

Of course, this might only work with types that specifically implement a property for Empty, such as dictionary, list, etc.

[CyrusNajmabadi]

The collection-literals proposal (such were working on for the next version of c#) allows you to just use [] to represent 'empty' in all these cases.

[JustinMinnaar]

Does the collection-literals proposal use a single static instance of the empty collection, to prevent allocation memory on the heap for a new collection each time an empty is returned?

[JustinMinnaar]

That is an interesting thought. Can one mutate the existing Array.Empty<string>() result? Would we not just add a similar method, a new List.Empty<string>() method?

[CyrusNajmabadi]

No. You cannot add to arrays. But you can certainly add to lists. That's the defining difference between the two.

[saint4eva]

https://www.youtube.com/watch?v=xIA3t2Je3uQ

[KennethHoff]

Does this mean that the collection literals will lower to something akin to this?

List<int> intList = []; // new List<int>(0);
int[] intArray = []; // Array.Empty<int>();
Span<int> intSpan = []; // stackalloc Array.Empty<int>(); // This might be entirely wrong. Never used a Span 🤷 

[CyrusNajmabadi]

Yes