What is the difference between list[i] vs list.ToList()[i] in C#?

March 2, 2023

I am coming back to C# after a long time. Usually, when I want to get or set some value at a specific index, I use .list[i] but recently I have noticed .list.ToList()[i] pattern.

Question:

What is the difference OR advantage of that?

Code:

var randomWords = new List<string>{ "abc", "def", "ghi"};

for (int i = 0; i < randomWords.Count; i++)
{
  Console.WriteLine(randomWords[i]); 
  Console.WriteLine(randomWords.ToList()[i]);
}

Output:

abc
abc
def
def
ghi
ghi

>Solution :

ToList() is a Linq extension method that will create a List<T> from any IEnumerable<T>, such as arrays, lists, or even a query that needs to be executed.

If you call it on something that’s already a List<T>, it will create a copy of that list and get the ith element, which is not functionally different other than you’re working with a shallow copy of the list.

Without knowing what .list is it’s hard to know why someone would do that – perhaps .list is a poorly named property of a type that does not have an indexed, or a lazy-loaded query?

If .list is already a list or has an indexer, I see no benefit of creating another list just to call the indexer.

Even if .list did not have an indexer, there are more efficient ways to get the ith element without creating a list.