C# Online Compiler | .NET Fiddle

// Author : Tech Point Fundamentals
// Website : www.techpointfunda.com
// Demo : Interface Partial Methods Demo in C# 8

using System;

// Declaring delegate
public delegate void PartialMethoDelegate();

public partial interface IUser
{
	partial void GetUserName(); // Partial method declaration
	partial void GetUserName(ref string name, int userId); // Method overloading

	static partial void GetUserEmail(); // Partial method declaration
	partial void GetUserPhoneNumber(); // Partial method declared but not implemented

	partial void GetdataTypeName<T>(T type);

	partial void GetUserName() // Partial method implementation in same partial type
	{
		Console.WriteLine("Tech Point Fundamentals");
	}

	public void GetUserDetails()
	{		
		PartialMethoDelegate _getUserName = new PartialMethoDelegate(GetUserName); // Instantiating delegate
		_getUserName(); // Calling delegate		

		string _userName = "";
		GetUserName(ref _userName, 1);
		Console.WriteLine("User Name By Id: " + _userName);		

		GetUserEmail();
		GetUserPhoneNumber(); // Calling partial method which is not defined
		GetdataTypeName<int>(5); // Calling generic partial method 
		GetdataTypeName<double>(5.8); // Calling generic partial method		
	}

}

partial interface IUser
{
	partial void GetUserName(ref string name, int userId)
	{
		if(userId == 1)
		{
			name = "Tech Point Funda";
		}
		else
		{
			name = "";
		}
	}	
	static partial void GetUserEmail()
	{
		Console.WriteLine("help@techpointfundamentals.com");
	}	

	partial void GetdataTypeName<T>(T type)
	{
		Console.WriteLine("Data Type of '" + type + "' is : " + type.GetType().FullName);
	}
}

partial class User : IUser
{	
} 

public class Program
{		
	public static void Main()
	{
		IUser _iUser = new User();
		_iUser.GetUserDetails();
	}
}

 
// Author : Tech Point Fundamentals
// Website : www.techpointfunda.com
// Demo : Interface Partial Methods Demo in C# 8
​
using System;
​
// Declaring delegate
public delegate void PartialMethoDelegate();
​
public partial interface IUser
{
    partial void GetUserName(); // Partial method declaration
    partial void GetUserName(ref string name, int userId); // Method overloading
​
    static partial void GetUserEmail(); // Partial method declaration
    partial void GetUserPhoneNumber(); // Partial method declared but not implemented
​
    partial void GetdataTypeName<T>(T type);
​
    partial void GetUserName() // Partial method implementation in same partial type
    {
        Console.WriteLine("Tech Point Fundamentals");
    }
​