New Features Of C# 7.0

C# 7.0 adds a number of new features and focuses on data consumption, code simplification and performance. To play demo, you need to use visual studio 2017 to create a new console project, then modify your code as below

Out variables

In C# version < 7.0, you need to declare x variable outside the TryParse method

int x;
if (int.TryParse(Console.ReadLine(), out int x))
{
    Console.WriteLine($"Your number: {x}");
}

In C# 7.0 you can modify code as below

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Please enter a number: ");
            if (int.TryParse(Console.ReadLine(), out int x))
            {
                Console.WriteLine($"Your number: {x}");
            }
            Console.ReadLine();
        }
    }
}

Local functions

Local functions are private methods of nested type in another member. They can only be called from their containing member.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            int Add(int x, int y)
            {
                return x + y;
            }
            Console.WriteLine($"x + y = {Add(2, 3)}");
            Console.ReadLine();
        }
    }
}

Discards

C# 7.0 allows you to use discard and the returned value which is not required. Using _ character for discarding the parameter. The discard parameter is also referred as write-only and you can't read the value from this parameter.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp
{
    class Customer { }

    class Program
    {
        static void Main(string[] args)
        {
            dynamic a;
            a = 1;
            //a = "c# code";
            //a = null;
            //a = new Customer();
            if (a is int)
                Console.WriteLine("a is int");
            else if (a is null)
                Console.WriteLine("a is null");
            else if (a is string)
                Console.WriteLine("a is string");
            else if (a is var _)
                Console.WriteLine("unknown");
            Console.ReadLine();
        }
    }
}

Pattern Matching

This is one of the most popular features of C# 7.0. As you can see in the example below, GetData method write in C# version < 7.0

public void GetData(dynamic value)
{
    if (value is Student)
    {  
        var s = value as Student;
        Console.WriteLine($"Student Id : {s.Id} Student Name {s.FullName}");
    }
    if (value is Professor)
    {  
        var p = p as Professor;
        Console.WriteLine($"Professor Id : {p.Id} Professor Name {p.FullName}");
    }  
    else
        Console.WriteLine("Unknown !");
}

In C# 7.0 you can modify code as below

public void GetData(dynamic value)
{
    if (value is Student s)
        Console.WriteLine($"Student Id : {s.Id} Student Name {s.FullName}");
    if (value is Professor p)
        Console.WriteLine($"Professor Id : {p.Id} Professor Name {p.FullName}");
    else
        Console.WriteLine("Unknown !");
}

Tuple

A tuple is a data structure that has a specific number and sequence of elements. As you can see in the example below, GetProductPrice method write in C# version < 7.0

static Tuple<decimal, decimal> GetProductPrice(int id)
{
    //Find product by id, then return price & discount
    return new Tuple<decimal, decimal>(100, 10);
}

static void Main(string[] args)
{
    var product = GetProductPrice(1);
    Console.WriteLine($"Price {product.Item1}$, Discount {product.Item2}%");
    Console.ReadLine();
}

You need install System.ValueTuple from nuget. You can rewrite the code above with C# 7.0 as below

static (decimal, decimal) GetProductPrice(int id)
{
    //Find product by id, then return price & discount
    return (100, 10);
}