Visual Studio 2017 - C# 7.0 Features

1. Out Variables

static void Main(string[] args)
{
    string first = "M";
    string last = "K";
    string name = string.Empty; //have to pre-declare before using the out.
    GetName(first, last, out name);

    //In c# 7.0, you can declare in the variable line
    GetName(first, last, out string name1);
    GetName(first, last, out var name2); ////use var instead of string
}

static void GetName(string first, string last, out string name)
{
    name = first + " " + last;
}

2. Pattern Matching

class Program
{
static void Main(string[] args)
{
Contact hr = new HR();
PatternMatching(hr); // hr.CreateEmployee(); will execute

Contact tm = new Manager("Emp 2", 2, "IT");
PatternMatching(tm); //teamManager.ContactTeamManager(); will execute

Contact pm = new Manager("Emp 3", 3, "PM");
PatternMatching(pm); // projectManager.ContactProjectManager(); will execute

Contact c = new Contact();
PatternMatching(c); // Console.WriteLine("Contract employee"); will execute

PatternMatching(null); //throw new ArgumentNullException(nameof(contact)); will execute
}

static void PatternMatching(Contact contact)
{
switch (contact)
{
case HR hr: //Syntax error, ':' expected, old version
hr.CreateEmployee();
break;

case Manager teamManager when (teamManager.Department == "IT"): //Expected ; or = (cannot specify constructor arguments in declaration)
teamManager.ContactTeamManager();
break;
case Manager projectManager:
projectManager.ContactProjectManager();
break;
default:
Console.WriteLine("Contract employee");
break;
case null:
throw new ArgumentNullException(nameof(contact));
}
}
}

public class Contact
{
public string Name { get; set; }
public int  ID { get; set; }
public string Department { get; set; }
}
public class HR : Contact {

public HR()
{
this.Name = "Emp 1";
this.ID = 1;
this.Department = "HR";
}

public void CreateEmployee() { }
}

public class Manager : Contact
{
public Manager(string name, int id, string department)
{
this.Name = name;
this.ID = id;
this.Department = department;
}

public void ContactTeamManager() { }

public void ContactProjectManager() { }
}

3. Is-Expressions

void GetID(object empID)
{
//older version, error  The name 'iEmpID'  or 'sEmpID' does not exist in the current context
if (empID is int iEmpID || (empID is string sEmpID &&
int.TryParse(sEmpID, out iEmpID)))
{
Console.WriteLine(iEmpID);
}
}

GetID(5);
GetID("5");

Code will accept the 'id' of employee as either a string or an integer.
The 'empId' is an integer, immediately execute the boyd of if statement body.
The 'empId' is a string, using the int.TryParse method to convert string to int.

TryParse the out variable must be defined before the statment, but C# 7.0, no longer to define

4. Tuples

By assigning each member to a value
var alpha = ("A", "B", "c");
Console.WriteLine(alpha.Item1 + " - " + alpha.Item2 + " - " + alpha.Item3);
         
By providing semantic names to each members to a value. Sematic names exist only at compile time.
(string first, string last, string middle) names = ("Day", "Night", "Soft");
//OR (string first, string last, string middle) names = EmployeeName(100);
Console.WriteLine(names.first + " - " + names.last + " - " + names.middle);

//throw error - The contextual keyword 'var' may only appear within a local variable declaration or in script code
//(var first, var last, var middle) names = LookupName(100);
//var (first, last, middle) names = LookupName(100);
//string (first, last, middle) names = EmployeeName(100);
//(first, last, middle) names = EmployeeName(100);


By providing semantic names on the right side of the assignment.
var names1 = (first:"Day", last:"Night", middle:"Soft");
Console.WriteLine(names1.first + " - " + names1.last + " - " + names1.middle);

//warning message - The tuple element name 'firstName' is ignored because a different name or no name is specified by the target type '(string first, string last, string middle)'.
(string first, string last, string middle) names2 = (firstName: "Day", lastName: "Night", middleName: "Soft");
Console.WriteLine(names2.first + " - " + names2.last + " - " + names2.middle);


public static (string, string, string) EmployeeName(int empID) // tuple return type
{
    var fn = "Day";
    var mn = "Night";
    var ln = "Soft";

    return (fn, mn, ln);
}

5. Digit Separators

long d = 1234567;
//OR long d1 = 1_234_567; //it would be represented as 1,234,567.
//The compiler will ignore the underscores at build time.

Console.WriteLine(d + " - " + d1); //both same output

var xv = 0xAB_CD_EF; //11259375
//OR var xv1 = 0xABCDEF; //11259375
Console.WriteLine(xv + " - " + xv1); //both same output

var bv1 = 0b1101_0101_0100_0011_0010_0001; //13976353
//OR var bv2 = 0b110101010100001100100001;
Console.WriteLine(bv1 + " - " + bv2); //both same output

6. Throw Exceptions -  can be use conditional, null coalescing and lambda expressions.

public static string GetName(string id)
{
    //Old version
    /*if (id == null)
throw new Exception("Name not found");
    return "F L";*/

    //Throw Exceptions can be use conditional, null coalescing and lambda expressions.
    return "F L" ?? throw new Exception("Name not found");
}