All 16 Collections questions
More in Collections
When would you use a List<T> vs an array? When should you use a Dictionary<TKey,TValue>? What is the difference between List<T> and an array (T[]) in terms of resizing? What is the difference between Dictionary<TKey, TValue> and List<T> in terms of lookup performance? What does HashSet<T> provide and when do you use it? When would you choose a HashSet<T> over a List<T>, and what guarantee does it provide? How does Queue<T> differ from Stack<T> in terms of the order items are removed? What is the difference between IEnumerable<T>, ICollection<T>, and IList<T> in the collection interface hierarchy? When would you reach for a ConcurrentDictionary or an immutable collection? How do you avoid multiple enumeration of an IEnumerable?
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C# › Collections

What is the difference between IEnumerable, ICollection and IList?

Intermediate

Answer

IEnumerable supports iteration only; ICollection adds Count/Add/Remove; IList adds indexed access and Insert. Accept the least specific type your method needs.
void Print(IEnumerable<int> xs) {}
int First(IList<int> xs) => xs[0];
Real-world example Accepting IEnumerable<T> in APIs keeps callers flexible (arrays, lists, LINQ).
All 16 Collections questions