Why is Dictionary preferred over Hashtable in C#?

In modern C# development, Dictionary<TKey, TValue> (often referred to simply as Dictionary) is generally preferred over Hashtable for several key reasons. While Hashtable is an older collection class from the early .NET days, Dictionary<TKey, TValue> offers improvements that make it more efficient, type-safe, and developer-friendly.

1. Generics and Type Safety

Strongly Typed: Dictionary<TKey, TValue> uses generics, allowing you to specify exact key and value types. This eliminates the need for casting objects, reducing the risk of runtime errors.
No Boxing/Unboxing: With generics, you avoid boxing (wrapping value types in object) and unboxing (extracting them back), improving performance and readability.

// Dictionary usage: strongly typed
var dict = new Dictionary<int, string>();
dict[1] = "One";
dict[2] = "Two";

// Hashtable usage: not strongly typed
var table = new Hashtable();
table[1] = "One";
table[2] = "Two"; // compiler won't prevent table[2] = 123;

2. Performance

Optimized Internals: Dictionary<TKey, TValue> uses more optimized hashing algorithms for various key types, which can lead to faster lookups than Hashtable.
No Casting Overhead: Because Hashtable stores everything as object, accessing elements typically involves casting. Dictionary<TKey, TValue> avoids this overhead for value-type lookups and insertions.

3. Readability and Maintenance

Clear Intent: A dictionary states explicitly what types it holds, making the code more self-documenting.
Reduced Errors: With strong type checking at compile time, you’re less likely to accidentally store or retrieve a key or value of the wrong type.

4. Modern API Features

Linq and Extension Methods: Dictionary<TKey, TValue> is fully integrated with .NET’s generic collections ecosystem. You can easily use LINQ queries (.Where(), .Select(), etc.) without extra conversions.
Iterators: For dictionary enumeration, KeyValuePair<TKey, TValue> is strongly typed, making iteration more straightforward and less error-prone.

When Might You Still Use `Hashtable`?

Hashtable might appear in legacy .NET Framework code or in certain reflection-based scenarios, but even then, most developers refactor to Dictionary<TKey, TValue> for the above advantages. There’s rarely a modern scenario where Hashtable is the better option.

Elevate Your C# and System Design Expertise

Choosing the right data structure is fundamental in technical interviews and professional software development. If you want to strengthen your problem-solving techniques and system design knowledge, consider these resources from DesignGurus.io:

Grokking the Coding Interview: Patterns for Coding Questions
Grokking System Design Fundamentals (for a beginner-friendly system design overview)
Grokking the System Design Interview (to prepare for intricate system design interviews)

You can also find free tutorials and in-depth discussions on coding and system design on the DesignGurus.io YouTube channel. By using modern collection types like Dictionary, you’ll write cleaner, more efficient, and more maintainable C# code.

CONTRIBUTOR

TechGrind