Дмитрий Верескун «Синтаксический сахар C#»

1.NET Meetup 2017 Syntactic sugar of C#
SEP 30, 2017
Syntactic sugar of C#:
language
improvements in
latest versions
by Dmitry Vereskun

• Properties enhancements
• Lambda expressions
• Initializers
• Number literals
• Inline variables
• Null expressions
• Throw expression
• Local functions
• Ref locals and ref returns
• Value tuples
• Pattern matching
• Async improvements
• Default keyword
AGENDA
C# 6.0 (VS 2015)
C# 7.0 (VS 2017)
C# 7.1 (VS 2017.3)
6
7
7.1

PROPERTIES
private string _value;
public string GetValue()
{
return _value;
}
public void SetValue(string value)
{
_value = value;
}
public string Value
{
get
{
return _value;
}
set
{
_value = value;
}
}

AUTO-PROPERTIES
public string Value
{
get
{
return _value;
}
set
{
_value = value;
}
}
public string Value
{
get;
set;
}
public string Value { get; set; }
or

GETTER-ONLY PROPERTIES AND METHODS
public string DoubleValue
{
get
{
return _value * 2;
}
}
public string DoubleValue => _value * 2;
public int GetResult()
{
return evaluate_result();
}
public int GetResult()
=> evaluate_result();
6

LAMBDAS EVERYWHERE
public string Value
{
get
{
return _value;
}
set
{
_value = value;
}
}
public string Value
{
get => _value;
set => _value = value;
}
public MyClass(int n)
{
_n = n;
}
public MyClass(int n) => _n = n;
7

AUTO-PROPERTY INITIALIZERS AND READ-ONLY PROPERTIES
private string _value = "N/A";
public string Value
{
get
{
return _value;
}
set
{
_value = value;
}
}
public string Value { get; set; } = "N/A";
6
private readonly int _onlyFive = 5;
public int OnlyFive
{
get
{
return _onlyFive;
}
}
public int OnlyFive { get; } = 5;

SINGLETON IN 2 (OR 3) LINES OF CODE
public class Singleton
{
private Singleton() { }
public static Singleton Instance { get; } = new Singleton();
}
public class Singleton
{
private Singleton() { }
static Singleton() => Instance = new Singleton();
public static Singleton Instance { get; }
}
6

• Classic
• New
DICTIONARY INITIALIZERS
var capitals = new Dictionary<string, string>
{
{ "Russia", "Moscow" }, // call Add
{ "Belarus", "Minsk" },
{ "Ukraine", "Kyiv" },
{ "USA", "Washington, D.C." },
};
var capitals = new Dictionary<string, string>
{
["Russia"] = "Moscow", // use indexer
["Belarus"] = "Minsk",
["Ukraine"] = "Kyiv",
["USA"] = "Washington, D.C.",
};
6

• Type literals:
– float (2.3f)
– double (4d)
– decimal (12.6m)
– long (25L)
– uint (1000u)
– ulong (13ul)
• Integer literals:
– Decimal (123)
– Hexadecimal (0x7b)
• What’s new?
– Binary integer literal (0b01111011)
– Digit group separator: _
Works with any number literals (100_000)
NUMBER LITERALS
int maxValue = 2_147_483_647;
byte mask = 0b0111_10011;
7

• Before:
• After:
or
INLINE VARIABLES
int intValue;
if (int.TryParse(str, out intValue))
{
// some actions with intValue
}
if (int.TryParse(str, out int intValue))
{
}
if (int.TryParse(str, out var intValue))
{
}
7

• Null coalescing operator can be applied for any nullable types
NULL EXPRESSIONS » NULL COALESCING OPERATOR ??
string s = GetValue();
if (s == null) s = "Default value";
string s = GetValue() ?? "Default value";
int? parentId = reader["parentId"] as int?;
int pId = parentId.HasValue ? parentId.Value : -1;
int pId = (reader["parentId"] as int?) ?? -1;

• So called Safe navigation operator or Elvis operator
• If left operand is not null, the operator acts as a regular dot operator
• If left operand is null, it returns a default value for expected type
NULL EXPRESSIONS » NULL-CONDITIONAL OPERATOR ?.
Type of foo.bar Type of foo?.bar
void void
Nullable type (incl. reference types) Same nullable type
Non-nullable type (structs, enums) Nullable<T> wrapper
6

SAFE DELEGATE INVOCATION WITH NULL-CONDITIONAL OPERATOR
protected virtual void OnComplete()
{
EventHandler complete = Complete;
if (complete != null)
{
complete(this, EventArgs.Empty);
}
}
protected virtual void OnComplete()
=> Complete?.Invoke(this, EventArgs.Empty);

NULL EXPRESSIONS » NULL-CONDITIONAL OPERATOR ?.
if (user != null)
{
user.Show();
}
int? age = (user != null)
? user.Age
: default(int?);
string name = (user != null && user.Name != null)
? user.Name
: "Guest";
user?.Show();
int? age = user?.Age;
string name = user?.Name ?? "Guest";
6

NULL EXPRESSIONS » NULL-CONDITIONAL OPERATOR ?[]
User[] users = GetUsers();
if (users != null)
{
Show(users[0].Name);
}
else
{
Show("no users");
}
Show(users?[0].Name ?? "no users");
if (users != null && users.Length > 0)
{
Show(users[0].Name);
}
else
{
Show("no users");
}
Show(users?.FirstOrDefault()?.Name);
6

• Throw can be placed in any place instead of ordinary expression
• Best to union it with ?: or ?? operators
THROW EXPRESSION
if (name == null)
{
throw new ArgumentNullException(nameof(name));
}
this.name = name;
this.name = name ?? throw new ArgumentNullException(nameof(name));
string first = args?.Length > 0
? args[0]
: throw new ArgumentException("Array is null or empty", nameof(args));
7

LOCAL FUNCTIONS
public static void QuickSort(int[] arr)
{
if (arr == null) throw new ArgumentNullException(nameof(arr));
if (arr.Length == 0) return;
SortSegment(0, arr.Length - 1);
void SortSegment(int from, int to)
{ … }
void SwapAndMove(ref int i, ref int j)
{ … }
}
{
int temp = arr[i];
arr[i++] = arr[j];
arr[j--] = temp;
}
{
int mid = arr[from + (to - from) / 2],
i = from, j = to;
while (i <= j)
{
while (arr[i] < mid) i++;
while (arr[j] > mid) j--;
if (i <= j) SwapAndMove(ref i, ref j);
}
if (i < to) SortSegment(i, to);
if (from < j) SortSegment(from, j);
}
7

public static void QuickSort(int[] arr)
{
if (arr == null) throw new ArgumentNullException(nameof(arr));
if (arr.Length == 0) return;
SortSegment(0, arr.Length - 1);
{
int mid = arr[from + (to - from) / 2], i = from, j = to;
while (i <= j)
{
while (arr[i] < mid) i++;
while (arr[j] > mid) j--;
if (i <= j) SwapAndMove(ref i, ref j);
}
if (i < to) SortSegment(i, to);
if (from < j) SortSegment(from, j);
}
{
int temp = arr[i];
arr[i++] = arr[j];
arr[j--] = temp;
}
}
Complete QuickSort with local functions

REF LOCALS AND REF RETURNS
private static ref int Max(ref int x, ref int y)
{
if (x > y)
{
return ref x;
}
else
{
return ref y;
}
}
int a = 123;
int b = 456;
Max(ref a, ref b) += 100;
Console.WriteLine(b); // 556!
7

REF LOCALS AND REF RETURNS
private static ref int Max(int[] array)
{
int max = 0;
for (int i = 1; i < array.Length; i++)
{
if (array[i] > array[max]) max = i;
}
return ref array[max];
}
int[] arr = { 3, 1, 4, 1, 5, 9, 2, 6, 5 };
Max(arr) = 0;
7

VALUE TUPLES
private static (int min, int max) MinAndMax(int[] array)
{
int min = array[0], max = min;
for (int i = 1; i < array.Length; i++)
{
if (array[i] < min) min = array[i];
if (array[i] > max) max = array[i];
}
return (min, max);
}
int[] arr = { 1, 4, 3, 6, 5, 8, 9 };
var minMax = MinAndMax(arr); // minMax.min and minMax.max
(int min, int max) minMax = MinAndMax(arr); // same as previous
(int, int) minMax = MinAndMax(arr); // minMax.Item1 and minMax.Item2
(int min, int max) = MinAndMax(arr); // min and max — deconstruction
(int min, _) = MinAndMax(arr); // min only
7

TUPLE ELEMENT NAMES INFERENCE
int count = 5;
string label = "Colors used in the map";
var pair = (count: count, label: label);
// old good C# 7.0. You have to define properties’ names
7.1
int count = 5;
string label = "Colors used in the map";
var pair = (count, label);
// element names are "count" and "label“. Inferred in C# 7.1

VALUE TUPLE DECONSTRUCTION
public class Point
{
public int X { get; set; }
public int Y { get; set; }
public void Deconstruct(out int x, out int y)
{
x = X;
y = Y;
}
}
Point p = GetPoint();
(int x, int y) = p; // deconstruction
7

ORDINARY CLASS, NOTHING STRANGE… OH, WAIT~
public class Point
{
public static bool operator ==(Point p1, Point p2)
=> p1.X == p2.X && p1.Y == p2.Y;
public static bool operator !=(Point p1, Point p2)
=> !(p1 == p2);
public override bool Equals(object obj)
{
Point p = obj as Point;
return (p != null && this == p);
}
public override int GetHashCode() => X ^ Y;
}

ORDINARY CLASS, NOTHING STRANGE… OH, WAIT~
public class Point
{
=> p1.X == p2.X && p1.Y == p2.Y;
=> !(p1 == p2);
{
return (p != null && this == p);
}
}

PATTERN MATCHING » NULL TEMPLATE
public class Point
{
=> p1.X == p2.X && p1.Y == p2.Y;
=> !(p1 == p2);
{
return !(p is null) && (this == p);
}
}
7

PATTERN MATCHING » TYPE TEMPLATE
public class Point
{
=> p1.X == p2.X && p1.Y == p2.Y;
=> !(p1 == p2);
{
return (obj is Point p) && (this == p);
}
}
7

PATTERN MATCHING
if (shape is null)
{
// show NULL error
}
else if (shape is Rectangle r)
{
// work with Rectangle r
}
else if (shape is Circle c)
{
// work with Circle c
}
7

PATTERN MATCHING
public static void SwitchPattern(object obj)
{
switch (obj)
{
case null:
Console.WriteLine("Constant pattern"); break;
case Person p when p.FirstName == "Dmitry":
Console.WriteLine("Person Dmitry"); break;
case Person p:
Console.WriteLine($"Other person {p.FirstName}, not Dmitry"); break;
case var x when x.GetType().IsGeneric:
Console.WriteLine($"Var pattern with generic type {x.GetType().Name}"); break;
case var x:
Console.WriteLine($"Var pattern with the type {x.GetType().Name}"); break;
}
}
7

GENERALIZED ASYNC RETURN
public async ValueTask<int> TakeFiveSlowly()
{
await Task.Delay(100);
return 5;
}
7
Now async methods can return ANY type with “async pattern”— GetAwaiter()

ASYNC MAIN
static int Main()
{
return DoAsyncWork().GetAwaiter().GetResult();
}
static async Task<int> Main()
{
return await DoAsyncWork();
}
static async Task Main()
{
await DoAsyncWork();
}
7.1

DEFAULT KEYWORD
Func<string, bool> whereClause = default(Func<string, bool>);
void SomeMethod(int? arg = default)
{
// ...
}
7.1
Func<string, bool> whereClause = default;

• C# 7.2
– Read-only references and structs
– Blittable types
– Ref-like types (stack only)
– Non-trailing named arguments
– Private protected access modifier
• C# 8
– Nullable reference types
– Default interface methods (who says Java?)
– Async streams
– Extension everything
WHAT ARE WE WAITING FOR?
https://channel9.msdn.com/Blogs/Seth-Juarez/A-Preview-of-C-8-with-Mads-Torgersen

Thanks for attention!
Questions? Suggestions?
Author: Dmitry Vereskun
ROKO Labs, Saratov, Russia
Telegram: d_vereskun

Дмитрий Верескун «Синтаксический сахар C#»

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