Type Checking: “typeof, GetType, or is” in C#?

In C#, typeof, GetType(), and the is keyword serve distinct purposes for type checking and type retrieval. Here’s when and how to use each:

1. is Operator (Type Compatibility Check)

• Purpose: Checks if an object is compatible with a type (including inheritance hierarchy).
• Usage:

  if (obj is MyClass) { ... } // Includes derived types
  if (obj is int) { ... }     // Works with value types (boxing handled)

• Key Points:
• Returns true for base classes or interfaces if the object implements them.
• Handles null safely (returns false if obj is null).
• Use for polymorphic checks (e.g., interface/abstract class validation).

2. GetType() (Exact Runtime Type)

• Purpose: Retrieves the exact runtime type of an object.
• Usage:

  Type type = obj.GetType();
  if (type == typeof(MyClass)) { ... } // Exact type match

• Key Points:
• Returns the actual type (ignores inheritance).
• Throws NullReferenceException if obj is null.
• Use for exact type checks (e.g., reflection, serialization).

3. typeof Operator (Type Metadata)

• Purpose: Retrieves the System.Type metadata for a compile-time known type.
• Usage:

  Type type = typeof(MyClass); // Compile-time resolution

• Key Points:
• Operates on type names (not variables).
• Use for reflection, attribute checks, or comparing against GetType().

Comparison Table

Feature	is	GetType()	typeof
Checks Inheritance	Yes ✅	No ❌	N/A
Handles null	Yes ✅	No ❌ (throws)	N/A
Works with Types	Yes (runtime check)	No (instance method)	Yes (compile-time type)
Performance	Fast (compiler-optimized)	Slightly slower	Compile-time resolution

When to Use Which?

• Polymorphic Checks:

  if (animal is Dog) { ... } // Check if `animal` is a Dog or subclass.

• Exact Type Matching:

  if (obj.GetType() == typeof(Dog)) { ... } // Only true for Dog, not subclasses.

• Reflection/Attributes:

  var methods = typeof(MyClass).GetMethods(); // Get metadata for MyClass.

Example Workflow

object obj = new GoldenRetriever(); // GoldenRetriever inherits from Dog

// Check compatibility (inheritance-aware)
if (obj is Dog) { ... } // ✅ True

// Check exact type
if (obj.GetType() == typeof(Dog)) { ... } // ❌ False (actual type is GoldenRetriever)

// Get Type metadata
Type dogType = typeof(Dog);

Summary:

• Use is for polymorphic or interface-based checks.
• Use GetType() for exact runtime type comparisons.
• Use typeof to retrieve compile-time type metadata.