C# : Interview questions (91-95)

 Questions:

• How do you implement a switch statement with pattern matching in C#?
• What are attributes in C#?
• How do you define custom attributes in C#?
• Explain the use of reflection in C#.
• What is the difference between "typeof" and "GetType()" in C#?

C# : Interview questions (86-90)

Answers:

1. Implementing a Switch Statement with Pattern Matching in C#:

Pattern matching in switch statements allows you to match against the type and properties of an object. This can make your code more readable and expressive.

public abstract class Shape { }

public class Circle : Shape
{
    public double Radius { get; set; }
}

public class Rectangle : Shape
{
    public double Width { get; set; }
    public double Height { get; set; }
}

public static string GetShapeInfo(Shape shape)
{
    return shape switch
    {
        Circle c => $"Circle with radius {c.Radius}",
        Rectangle r => $"Rectangle with width {r.Width} and height {r.Height}",
        _ => "Unknown shape"
    };
}

// Usage
Shape shape1 = new Circle { Radius = 5.0 };
Shape shape2 = new Rectangle { Width = 4.0, Height = 6.0 };
Shape shape3 = new Shape();

Console.WriteLine(GetShapeInfo(shape1)); // Output: Circle with radius 5
Console.WriteLine(GetShapeInfo(shape2)); // Output: Rectangle with width 4 and height 6
Console.WriteLine(GetShapeInfo(shape3)); // Output: Unknown shape

In this example, the GetShapeInfo method uses a switch expression with pattern matching to determine the type of shape and extract its properties.

2. Attributes in C#:

Attributes in C# are metadata annotations that provide additional information about program elements such as classes, methods, and properties. They can be used for various purposes like controlling serialization, specifying documentation, or providing hints to the compiler.

3. Defining Custom Attributes in C#:

To define a custom attribute, you create a class that inherits from System.Attribute.

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
public class AuthorAttribute : Attribute
{
    public string Name { get; }
    public double Version { get; }

    public AuthorAttribute(string name, double version)
    {
        Name = name;
        Version = version;
    }
}

// Applying the custom attribute
[Author("John Doe", 1.0)]
public class SampleClass
{
    [Author("Jane Smith", 1.1)]
    public void SampleMethod() { }
}

In this example, the AuthorAttribute class is defined with Name and Version properties. The attribute is then applied to a class and a method.

4. Use of Reflection in C#:

Reflection in C# allows you to inspect and interact with metadata about types at runtime. It can be used to examine the contents of an assembly, create instances of types, and invoke methods.

using System;
using System.Reflection;

public class SampleClass
{
    public void PrintMessage(string message)
    {
        Console.WriteLine(message);
    }
}

// Usage
Type type = typeof(SampleClass);
MethodInfo methodInfo = type.GetMethod("PrintMessage");
object instance = Activator.CreateInstance(type);
methodInfo.Invoke(instance, new object[] { "Hello, Reflection!" });
// Output: Hello, Reflection!

In this example, reflection is used to get the PrintMessage method of the SampleClass type, create an instance of SampleClass, and invoke the PrintMessage method with a parameter.

5. Difference Between typeof and GetType() in C#:

• typeof: Used to get the Type object for a type at compile-time.

Type type = typeof(SampleClass);
Console.WriteLine(type.Name); // Output: SampleClass

• GetType(): Used to get the Type object for an instance at runtime.

SampleClass instance = new SampleClass();
Type type = instance.GetType();
Console.WriteLine(type.Name); // Output: SampleClass

In summary, typeof is used with type names to get the Type object at compile-time, while GetType() is called on an instance to get its Type object at runtime.

These explanations and examples should help you understand how to implement a switch statement with pattern matching, define and use custom attributes, use reflection, and the differences between typeof and GetType() in C#.

C# : Interview questions (96-100)