Where to use string [] vs list <string> in C#

Question

String[] is light weight compared to list<string>. So if I don't have any need to manipulate my collection, should I use string[] or is it always advisable to go for list<string>?

In case of list<string>, do we need to perform null check or not required?

Answer 1

Use string[] when you need to work with static arrays: you don't need to add and remove elements -> only access elements by index. If you need to modify the collection use List<string>. And if you intend to only loop through the contents and never access by index use IEnumerable<string>.

Answer 2

If the collection should not be modified, use string[] or even better, IEnumerable<string>. This indicates that the collection of strings should be treated as a read-only collection of strings.

Using IEnumerable<string> in your API also opens up for the underlying implementation to be changed without breaking client code. You can easily use a string array as the underlying implementation and expose it as IEnumerable<string>. If the implementation at a later stage is better suited using a list or other structure, you can change it as long as it supports IEnumerable<string>.