[Feature Request] implement __getitem__ for ListLiteral

[kiran-4444]

Review Mojo's priorities

• I have read the roadmap and priorities and I believe this request falls within the priorities.

What is your request?

I see this issue being referred in #100 and few other places, but __getitem__ isn't still implemented (or at least I wasn't able to access an item using it's index in a ListLiteral).

What is your motivation for this change?

I'm trying to work on #2018 and found that I need to iterate through a list of possible env variables that define the temp dirs names. But I'm surprised that I can't access the list items using their indices:

fn _candidate_tempdir_list() raises:
    var dirlist = []

    var env_vars = ["TMPDIR", "TEMP", "TMP"]
    for i in range(len(env_vars)):
        var env_var = env_vars.get(i)

Any other details?

I'd like to implement this if someone else isn't already working on this.

[melodyogonna]

I don't think that is a thing. Where would it be useful?

[kiran-4444]

This, I'm using to implement the code from: https://github.com/python/cpython/blob/main/Lib/tempfile.py#L156-L181

Basically, I'm thinking of a bit solid implementation for tempfile and tempdir just like Python's implementation.

[kiran-4444]

Should I go ahead with the implementation?

[artemiogr97]

@kiran-4444 for #2018 I guess you could simply iterate over a list for now, the following code prints all the elements of the list:

fn main():
    var my_vars = List("PATH", "TEMP")
    var index: Int
    for index in range(len(my_vars)):
        print(my_vars[index])

I agree that iterating over a ListLiteral is usefull but is not blocking for the other issue

[helehex]

ListLiteral is heterogeneous, meaning the elements it contains can have different types, and the type at each index is known at compile time. Also, since it's meant to be a literal type, it cant be changed in any way at runtime.

You should be able to do something like this though:
ListLiteral("Hi", "Kiran", "-4444").get[1,StringLiteral]() should return "kiran"

Maybe you could use a regular List for what you want to do?
List("Hi", "Kiran", "-4444")[1] should return "kiran"

It might be tricky to promote ListLiteral to a List currently due to their generics. This will be changing eventually though.
Also, for autopromotion you might need something like this

[guna-sd]

In Python, we can initialize a list with a simple syntax like this:

a = [1, 2, 'a']

Mojo offers a similar initialization syntax for a list literal:

var a = [1, 2, 'a']

However, there are some key differences between Python lists and Mojo's list literals. Python lists support a wide range of operations, including indexing, slicing, getitem, setitem, and more. In contrast, Mojo's list literals currently lack these features, cannot be iterated over directly, and require a parametric index instead of an argument index.

While Mojo does support a List type that provides the necessary functionality for indexing, slicing, and iteration, the List type cannot be initialized using the same syntax as a list literal.

It would be great if Mojo's list literals could support the same operations as Python lists or if the List type could be initialized with the list literal syntax and also make sure that mojo listliteral supports nested list like python nested list

[melodyogonna]

What is the plan for ListLiteral in general?