Attributes

Attributes provide a method for associating metadata with assemblies, classes, methods, properties, etc.

After an attribute is associated with an entity, the attribute can be queried at run time.

using System;

namespace LearnCSharp
{
    class Program
    {
        static void Main(string[] args)
        {
            // Get the attribute
            Attribute[] attrs = Attribute.GetCustomAttributes(typeof(Adder));
            foreach (Attribute attr in attrs)
            {
                if (attr is Developer)
                {
                    Developer developer = (Developer)attr;
                    Console.WriteLine($"{developer.GetName()} wrote the class {nameof(Adder)}");
                }
            }
        }
    }
}
// Use the attribute
[Developer("Anil")]
public class Adder
{
    public int Execute(int x, int y)
    {
        return x + y;
    }
}
// Create an attribute
[AttributeUsage(AttributeTargets.Class)]
public class Developer : Attribute
{
    private string Name;

    public Developer(string name)
    {
        Name = name;
    }

    public string GetName()
    {
        return Name;
    }
}

Output

Anil wrote the class Adder

The Developer attribute has a property called Name that we will use to identity the developer who wrote a class.

We add the attribute to the Adder class and specify the name of the developer who wrote the class as metadata for the class.

Finally, we locate the Developer custom attribute for the Adder class and use it to print the name of the developer who wrote the class in the console window.