C# Feature – Indexers

Overview

Indexers let instances be indexed like arrays, e.g., obj[key].

Introduced In

C# 1 (2002)

Before

public string GetByKey(string key) { /* ... */ }

After

public string this[string key] { get => Lookup(key); set => Store(key, value); }

Annotated Example

public class DictLike
{
  private readonly Dictionary<string,string> _m = new();
  public string this[string k] { get => _m[k]; set => _m[k] = value; }
}

Gotchas & Best Practices

• Use clear argument names/types; document behaviors for missing keys.

Related Features

• Properties & Events

Version Notes

• Works with spans/index/range (C# 8+) on indexer types.