Code to paste

/// Module: todo_list
module todo_list::todo_list;

use std::string::String;
use sui::transfer;

/// List of todos. Can be managed by the owner and shared with others.
public struct TodoList has key, store {
    id: UID,
    items: vector<String>
}

/// Create a new todo list and transfer it to the caller.
public entry fun new(ctx: &mut TxContext) {
    let list = TodoList {
        id: object::new(ctx),
        items: vector[]
    };
    
    transfer::transfer(list, ctx.sender());
}

/// Add a new todo item to the list.
public fun add(list: &mut TodoList, item: String) {
    list.items.push_back(item);
}

/// Remove a todo item from the list by index.
public entry fun remove(list: &mut TodoList, index: u64): String {
    list.items.remove(index)
}

/// Delete the list and the capability to manage it.
public entry fun delete(list: TodoList) {
    let TodoList { id, items: _ } = list;
    id.delete();
}

/// Get the number of items in the list.
public entry fun length(list: &TodoList): u64 {
    list.items.length()
}

Now You Can Test Your Contract

With your updated new function that creates and transfers the TodoList, you can now call:

sui client call --package 0x99706b6e72e3caa12466519fad43a82bc6a4ea7b833100f803296034ef231b12 --module todo_list --function new

This should work without the "UnusedValueWithoutDrop" error because the new function now handles the transfer automatically. After creating a TodoList, you can:

Add items:

sui client call --package 0x99706b6e72e3caa12466519fad43a82bc6a4ea7b833100f803296034ef231b12 --module todo_list --function add --args <todo_list_object_id> "Buy groceries"

Check length:

sui client call --package 0x99706b6e72e3caa12466519fad43a82bc6a4ea7b833100f803296034ef231b12 --module todo_list --function length --args <todo_list_object_id>

Try creating a new TodoList now with the updated package ID! Remember to get it after calling the new function