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New Features in C# 7 with Visual Studio 2017

Added and Improvements New Features in C# 7.0 with Visual Studio 2017 -
1.     Added Binary Literal
2.     Added Digit Separators
3.     Added Pattern Matching
4.     Added Ref returns and ref Locals
5.     Added some Tuples Enhancement
6.     Local Function
7.     Throw Expressions
8.     Added some expression bodied members like constructor, destructor, getters and setters in C# 7
9.     Added some enhancement for out variables
10. Deconstruction

Binary Literals -Improvements
int[] numbers = { 1, 2, 4, 6, 12, 40 };
int[] numbers = { 0b1, 0b10, 0b100, 0b1000, 0b10000, 40 };

Digit Separators - Digit separators inside the numbers
Literal Digit Allows underscore (_) inside numbers
var x = 1234_5435;
var y = 0xABCD_EFG_IJ
int[] numbers = { 0b1, 0b10, 0b100, 0b1000, 0b1_0000, 4_0 };

Tuples -
If you want write a common method that returns more than one value. It is add tuple types and tuple literals.
1.     Anonymous types return
2.     Dynamic return type
3.     Custom-built transport type

Example 1 -
int[] numbers = { 0b1, 0b10, 0b100, 0b1000, 0b1_0000, 4_0 };
var tn = TallyNumber(numbers);

WriteLine($"Sum: {tn.Item1}, count: {tn.Item2}");

(int, int) TallyNumber(int[] values)
{
    var rest = (0, 0);

    return rest;
}

Example 2 -
int[] numbers = { 0b1, 0b10, 0b100, 0b1000, 0b1_0000, 4_0 };
var tn = TallyNumber(numbers);

WriteLine($"Sum: {tn.sum}, count: {tn.count}");

(int sum, int count) TallyNumber(int[] values)
{
    var rest = (s:0, c: 0);
    return rest;
}

Example 3 -
int[] numbers = { 0b1, 0b10, 0b100, 0b1000, 0b1_0000, 4_0 };
var(sum, count) = TallyNumber(numbers);

WriteLine($"Sum: {sum}, count: {count}");

(int sum, int count) TallyNumber(int[] values)
{
    var rest = (s:0, c: 0);
    foreach (var val in values)
    {
        rest = (rest.s + val, rest.c + 1);
    }

    return rest;
}

Example 4 -
int[] numbers = { 0b1, 0b10, 0b100, 0b1000, 0b1_0000, 4_0 };
var(sum, count) = TallyNumber(numbers);

WriteLine($"Sum: {sum}, count: {count}");

(int sum, int count) TallyNumber(int[] values)
{
    var rest = (s:0, c: 0);
    foreach (var val in values)
    {
        Add(val, 1);
    }

    return rest;
    void Add(int s, int c) { rest.s += s; rest.c += c; }
}

Local Functions –
Functions inside other function bodies that are called local function.

Example -
int[] numbers = { 0b1, 0b10, 0b100, 0b1000, 0b1_0000, 4_0 };
var(sum, count) = TallyNumber(numbers);

WriteLine($"Sum: {sum}, count: {count}");

(int sum, int count) TallyNumber(int[] values)
{
    var rest = (s:0, c: 0);
    foreach (var val in values)
    {
        Add(val, 1);
    }

    return rest;
    void Add(int s, int c) { rest.s += s; rest.c += c; }
}

Pattern Matching -
1.     Enhancing two existing patterns-
2.     Is-expressions with patterns
3.     Switch case clauses with patterns

Example 1 -
public void PrintDollers(object obj)
{
    if (obj is null) return;     // This is the constant pattern "null"!
    if (!(obj is int k)) return; // This is the type pattern "int k";
   
   WriteLine(new string('$', k));
}

Example 2 -
// Switch on anything lie premitive, string etc.
switch (shape)
{
    case Rectangle sh when(sh.Length == sh.Height): WriteLine($"{sh.Length} x {sh.Height} square");
        break;
    default:
        WriteLine("<unknown shape found!>");
        break;
    case null:
        throw new ArgumentNullException(nameof(shape));
}

Deconstruction -

Example for deconstructing declaration -
(string firstName, string middleName, string lastName) = SearchName(id1); //deconstructing declaration
WriteLine($"found {firstName} {lastName}.");

Example for var inside -
(var firstName, var middleName, var lastName) = SearchName(id1);

Example for var outside -
var(firstName, middleName, lastName) = SearchName(id1);

Example for deconstructing assignment -
(firstName, middleName, lastName) = SearchName(id2);

Ref Returns and Locals –
Returning Values by Reference and It is a Kind of Pointers!
public class User
{
    public int ID { get; set; }
    public int Age { get; set; }
    public string Name { get; set; }
    public string Adress { get; set; }
    public override string ToString() { return $"{ID},{Age},{Name},{Adress}"; }
}

public static ref User FindUser(User U, User[] UList)
{
    for (int j = 0; j < UList.Length; j++)
        if (UList[j].ID == U.ID)
            return ref UList[j];

    throw new IndexOutOfRangeException($"{nameof(U)} not found");
}

References -
https://blogs.msdn.microsoft.com/dotnet/2016/08/24/whats-new-in-csharp-7-0/
By Anil Singh | Rating of this article (*****)

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