C# 6.0 Language Features Explained

C# 6.0
What?! C# is Being Updated?
Filip Ekberg

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Filip Ekberg
C# MVP
http://fekberg.com
@fekberg
C# Smorgasbord
/ Copyright ©2014 3 by Readify Pty Ltd

http://en.wikipedia.org/wiki/C_Sharp_(programming_language)#History
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History of C#

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C# 2.0
› Generics
› Partial types
› Anonymous methods
› Iterators
› Nullable types
› Getter/Setter separate accessibility
› Static classes
› And more..
/ Copyright ©2014 5 by Readify Pty Ltd @fekberg

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C# 3.0
› Implicitly typed local variables
› Object and collection initializers
› Auto-properties
› Anonymous types
› Extension methods
› Query expressions
› Lambda expressions
› Expression trees
› And more..

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C# 4.0
› Dynamic binding
› Named and optional parameters
› Generic co-and contravariance
› And more..

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C# 5.0
› Asynchronous methods
› Caller info attributes

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The state of the Compiler
› It’s been a black box
› Roslyn to the rescue!
› .NET Compiler Platform
› Microsoft decides to re-write the compiler
› Compiler written in C#
› Easier to extend and maintain
› Open Source!

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C# 6.0 Overview
› Auto-property initializers
› Getter-only auto-properties
› Assignment to getter-only auto-properties
from constructor
› Parameter-less struct constructors
› Using Statements for Static Members
› Dictionary Initializer
› Await in catch/finally
› Exception filters
› Expression-bodied members
› Null propagation
› String interpolation
› nameofoperator
› And more..

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Auto-Property
Initializers

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Auto-property initializers in a
nutshell
class Person
{
public string Name { get; set; }
}
class Person
{
= "Anonymous";
public string Name { get; } = "Anonymous";
}

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nutshell
class Person
{
public string Name { get; }
public Person()
{
Name = "Filip";
}
}

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nutshell
class Person
{
private readonly string <Name>k__BackingField = "Filip";
public string Name
{
get
{
return this.<Name>k__BackingField;
}
}
}

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Parameter-less
struct
constructors

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Parameter-less struct
constructors in a nutshell
struct Point
{
public int X { get; }
public int Y { get; }
}
Read Only!
public Point()
{
X = 100;
Y = 100;
}

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Read Only!
struct Point
{
private readonly int <X>k__BackingField;
private readonly int <Y>k__BackingField;
public int X
{
get
{
return this.<X>k__BackingField;
}
}
public int Y
{
get
{
return this.<Y>k__BackingField;
}
}
public Point()
{
this.<X>k__BackingField = 100;
this.<Y>k__BackingField = 100;
}
}

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Read Only!
struct Point
{
public int X { get; }
public int Y { get; }
public Point(int x, int y)
{
X = x;
Y = y;
}
public Point() : this(100, 100)
{
}
}

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Using
Statements for
Static Members

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Using Statements for Static
Members in a nutshell
class Program
{
static void Main(string[] args)
{
var angle = 90d;
Console.WriteLine(Math.Sin(angle));
}
}

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using System.Console;
using System.Math;
class Program
{
{
var angle = 90d;
WriteLine(Sin(angle));
}
}

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using System.Console;
using System.Linq.Enumerable;
class Program
{
{
foreach (var i in Range(0, 10))
{
WriteLine(i);
}
}
}

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Dictionary
Initializers

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Dictionary Initializers in a
nutshell
var people = new Dictionary<string, Person>
{
["Filip"] = new Person()
};
var answers = new Dictionary<int, string>
{
[42] = "the answer to life the universe and everything"
};

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Await inside
Finally block

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Await + Finally in a nutshell
public async Task DownloadAsync()
{
}
try
{ }
catch
{
await Task.Delay(2000);
}
finally
{
await Task.Delay(2000);
}

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Exception Filters

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Exception filters in a nutshell
try
{
throw new CustomException { Severity = 100 };
}
catch (CustomException ex) if (ex.Severity > 50)
{
Console.WriteLine("*BING BING* WARNING *BING BING*");
}
catch (CustomException ex)
{
Console.WriteLine("Whooops!");
}

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Null
Propagation

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Null propagation in a nutshell
class Person
{
public Address Address { get; set; }
}
class Address
{
public string AddressLine1 { get; set; }
}
var filip = new Person
{
Name = "Filip"
};
Console.WriteLine(filip.Address.AddressLine1);

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class Person
{
}
class Address
{
}
{
Name = "Filip"
};
Console.WriteLine(filip.Address.AddressLine1);

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class Person
{
}
class Address
{
}
{
Name = "Filip"
};
Console.WriteLine(filip.Address .=A=d dnruelslsL?i n"eN1o) ;Address" : filip.Address.AddressLine1);

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class Person
{
}
class Address
{
}
{
Name = "Filip"
};
Console.WriteLine(filip.Address .=A=d dnruelslsL?i n"eN1o) ;Address" : filip.Address.AddressLine1);
Console.WriteLine(filip?.Address?.AddressLine1 ?? "No Address");

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var people = new[]
{
new Person(),
null
};
WriteLine(people[0]?.Name);
WriteLine(people[1]?.Name);

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Person[] people = null;
WriteLine(people?[0]?.Name);
Person[] people = null;
Console.WriteLine(
(people != null) ?
((people[0] == null) ? null : people[0].Name)
: null
);

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Expression-bodied
members

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Expression-bodied members in
a nutshell
class Rectangle
{
public double Width { get; set; }
public double Height { get; set; }
public double Area => Width * Height;
}

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Expression-bodied members in
a nutshell
class Rectangle
{
public double Width { get; set; }
public double Height { get; set; }
public override string ToString() =>
"My Width is {Width} and my Height is {Height}";
}

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String
interpolation

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String interpolation in a
nutshell
Syntax will change in a later release to the following:
$"My Width is {Width} and my Height is {Height}";

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nutshell
public override string ToString()
{
object[] args = new object[] { this.Width, this.Height };
return string.Format("My Width is {0} and my Height is {1}", args);
}

int num = 28;
object[] objArray1 = new object[] { num };
Console.WriteLine(string.Format("Hello there, I'm {0:D5} years old!", objArray1));
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nutshell
int age = 28;
var result = "Hello there, I'm {age : D5} years old!";
WriteLine(result);

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nameof
operator

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nameof operator in a nutshell
{
WriteLine("Parameter name is: {nameof(args)}");
}

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nameof operator in a nutshell
public double CalculateArea(int width, int height)
{
if (width <= 0)
{
throw new ArgumentException("Parameter {nameof(width)} cannot be less than 0");
}
return width * height;
}

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Demo
C# 6.0 Language Features in Visual Studio 2015

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There’s more??

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What about C# 7.0?
› Binary literals and Digit separators
0b00001000
0xFF_00_FA_AF

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What about C# 7.0?
› Event initializers
var client = new WebClient
{
DownloadFileCompleted +=
DownloadFileCompletedHandler
};

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What about C# 7.0?
› Field targets on auto-properties
[field: NonSerialized]
public int Age { get; set; }

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What about C# 7.0?
› Semicolon operator
var y = (var x = Foo(); Write(x); x * x);

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What about C# 7.0?
› Using params with IEnumerable
int Avg(params IEnumerable<int> numbers)

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What about C# 7.0?
› Declaration Expressions
public void CalculateAgeBasedOn(int birthYear, out int age)
{
age = DateTime.Now.Year - birthYear;
}
CalculateAgeBasedOn(1987, out var age);

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What about C# 7.0?
› Declaration Expressions
› Primary Constructors
› And possibly more...
class Person(string name, int age)
{
private string _name = name;
private int _age = age;
}

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More with Roslyn
› Exposes the CompilerAPIs
› Plugins powered by Roslyn
› Analyze code
› Re-write code
@fekberg

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Summary
› C# 6.0 is awesome
› There’s a lot of change in C# 6.0
› .NET Compiler Platform ("Roslyn") makes it easy for Microsoft to
improve the language
› There’s a lot of interesting features that could go in C# 7.0
@fekberg

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Questions?

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Thank you!
http://fekberg.com
@fekberg
C# Smorgasbord

C# 6.0 Language Features Explained

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