Using coroutines as iterators

local function BasePartIterator(Table)
    local Length = #Table;
    local Thread = coroutine.create(function(_, Index)
        if (not Index) then --// If we're not passed an Index, make it 1;
            Index = 1;
        else
            Index = Index + 1; --// Otherwise increase it
        end

        for i = Index, Length do --// From the current Index to the Length
            if (Table[i]:IsA("BasePart")) then
                coroutine.yield(Table[i], i); --// These will be passed back again next iteration
            end
        end

        --// If none is found then it'll return nil, nil stops the for loop iterating
    end

    return function() --// Iterator
        local Success, BasePart, Index = coroutine.resume(Thread)
        return BasePart, Index;
    end
end

local WorkspaceDescendants = workspace:GetDescendants();
for BasePart, IndexFound in BasePartIterator(WorkspaceDescendants) do
    print(BasePart:IsA("BasePart")); --// Always true
    print(WorkspaceDescendants[i] == BasePart); --// Also always true
end