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C# Feature – Indexers

Overview

Section titled “Overview”

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

Introduced In

Section titled “Introduced In”

C# 1 (2002)

Before

Section titled “Before”
public string GetByKey(string key) { /* ... */ }

After

Section titled “After”
public string this[string key] { get => Lookup(key); set => Store(key, value); }

Annotated Example

Section titled “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

Section titled “Gotchas & Best Practices”
  • Use clear argument names/types; document behaviors for missing keys.
Section titled “Related Features”

Version Notes

Section titled “Version Notes”
  • Works with spans/index/range (C# 8+) on indexer types.