TDC2018SP | Trilha .Net - Novidades do C# 7 e 8

w w w. l a m b d a 3 . c o m . b r
Novidades do C# 7 e 8

Giovanni Bassi
• Programador
• Microsoft MVP
• Não gerente
• blog.lambda3.com.br, podcast.lambda3.com.br,
dotnetarchitects.net, nodebr, dockersp
@giovannibassi
/giggio.tech
• Escalador e ciclista

podcast.lambda3.com.br
0 – Eventos
1 – Docker
2 – .NET Core RC2
3 – Git
4 – Estudo
5 – Open Source
6 – Xamarin
7 – Node.js
8 – Democracia organizacional
9 – O programador poliglota
...
Toda semana em:

Acreditamos que a diversidade, em
suas diversas expressões, deve ser
respeitada e valorizada, e que uma
sociedade mais diversa é uma
sociedade melhor.
diversidade.tech

Código gerenciado
Generics
Language Integrated Query
Dinamismo + paridade nas linguagens
C# 5 + VB 11
Programação assíncrona
C# 1 + VB 7
C# 2 + VB 8
C# 3 + VB 9
C# 4 + VB 10
C# 6 + VB 14
Roslyn

Código gerenciado
Generics
C# 5 + VB 11
C# 1 + VB 7
C# 2 + VB 8
C# 3 + VB 9
C# 4 + VB 10
C# 6 + VB 14
Roslyn
C# 7 + VB 15
Features!

Código gerenciado
Generics
C# 5 + VB 11
C# 1 + VB 7
C# 2 + VB 8
C# 3 + VB 9
C# 4 + VB 10
C# 6 + VB 14
Roslyn
C# 7 + VB 15
Features! Features! Features!Features!

Código gerenciado
Generics
C# 5 + VB 11
C# 1 + VB 7
C# 2 + VB 8
C# 3 + VB 9
C# 4 + VB 10
C# 6 + VB 14
Roslyn
C# 7 + VB 15
Features! Features! Features!
Features (parte 2)?
C# 8 + VB 16?

https://insights.stackoverflow.com/survey/2018/#most-popular-technologies

F#
10,000’s
Tens of thousands
VB
100,000’s
Hundreds of thousands
C#
1,000,000’s
Millions

<PropertyGroup>
<LangVersion>latest</LangVersion>
</PropertyGroup>

public static int DiceSum(IEnumerable<object> values)
{
var sum = 0;
foreach (var item in values)
{
if (item is int val)
sum += val;
else if (item is IEnumerable<object> subList)
sum += DiceSum(subList);
}
return sum;
}
https://docs.microsoft.com/dotnet/csharp/pattern-matching
http://bit.ly/cspatternmatching

{
var sum = 0;
{
switch (item)
{
}
}
return sum;
}

case 0:
break;
case int val:
sum += val;
break;
case PercentileDie die:
sum += die.Multiplier * die.Value;
break;
{
var sum = 0;
{
switch (item)
{
}
}
return sum;
}

case 0:
break;
case int val:
sum += val;
break;
case PercentileDie die:
sum += die.Multiplier * die.Value;
break;
case IEnumerable<object> subList when subList.Any():
sum += DiceSum(subList);
break;
case IEnumerable<object> subList:
break;
case null:
break;
default:
throw new InvalidOperationException("unknown");
{
var sum = 0;
{
switch (item)
{
}
}
return sum;
}

void M()
{
var (name, company) = Person.Get();
WriteLine($"{name}, {company}");
}
class Person
{
public string Name { get; set; }
public string Company { get; set; }
public void Deconstruct(out string name, out string company)
{
name = Name;
company = Company;
}
public static Person Get() => new Person { Name = "…", Company = "…" };
} https://docs.microsoft.com/dotnet/csharp/tupleshttp://bit.ly/cstuplas

var numbers = (one: 1, two: 2);
var (uno, due) = numbers;
WriteLine($"{uno}, {due}");
https://docs.microsoft.com/dotnet/csharp/tuples
http://bit.ly/cstuplas

if (int.TryParse("1", out int result))
WriteLine(result);
if (int.TryParse("1", out var result2))
WriteLine(result2);
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#out-variables
http://bit.ly/csoutvars

(int x, int y) GetCoordinates() => (1, 2);
var (_, y) = GetCoordinates();
https://docs.microsoft.com/dotnet/csharp/discards
http://bit.ly/csdiscards

void ObjectDeconstruction()
{
var (name, _) = Person.Get();
}

if (int.TryParse("1", out _))
WriteLine("It is a number!");

object o = 1;
if (o is Person p)
WriteLine(p.Company);
else if (o is null)
WriteLine("null");
else if (o is var _)
WriteLine("Unknown");

ref int Find(int[,] matrix, Func<int, bool> predicate)
{
for (int i = 0; i < matrix.GetLength(0); i++)
for (int j = 0; j < matrix.GetLength(1); j++)
if (predicate(matrix[i, j]))
return ref matrix[i, j];
throw new InvalidOperationException("Not found");
}
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#ref-locals-and-returns
http://bit.ly/csreflocals

void M()
{
var matrix = new [,] { { 1, 2, 3, 4, 5 },
{ 6, 7, 8, 42, 10 } };
ref var item = ref Find(matrix, val => val == 42);
WriteLine(item);
item = 24;
WriteLine(matrix[1, 3]);
}
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#ref-locals-and-returns
http://bit.ly/csreflocals

public ExpressionBodiedMembers(string name) => Name = name;
~ExpressionBodiedMembers() => WriteLine("Finalized!");
private string name;
public string Name
{
get => name;
set => name = value;
}
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#more-expression-bodied-members
http://bit.ly/csmaisebm

private string a = GetA() ?? throw new Exception();
private static string GetA() => throw new Exception();
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#throw-expressions
http://bit.ly/csexpthrow

int sixteen = 0b0001_0000;
int thirtyTwo = 0b0010_0000;
int sixtyFour = 0b0100_0000;
int oneHundredTwentyEight = 0b1000_0000;
long oneHundredBillions = 100_000_000_000;
double AvogadroConstant = 6.022_140_857_747_474e23;
decimal GoldenRatio = 1.618_033_988_749M;
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#numeric-literal-syntax-improvements
http://bit.ly/csnumlit

double Average(IEnumerable<int> ns)
{
double Divide(double a, double b)
{
if (b == 0) throw new DivideByZeroException();
return a / b;
}
var sum = ns.Sum();
return Divide(sum, ns.Count());
}
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#local-functions
http://bit.ly/cslocalfunc

void Add1AndSumAll(int[] ms)
{
IEnumerable<int> Sum1(IEnumerable<int> ns)
{
foreach (var n in ns)
yield return n + 1;
}
if (ms == null) throw new NullReferenceException();
WriteLine(Sum1(ms).Sum());
}
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#local-functions
http://bit.ly/cslocalfunc

public async ValueTask<int> Get5()
{
await Task.Delay(100);
return 5;
}
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#generalized-async-return-types
http://bit.ly/csasyncgeneral

public async ValueTask<int> SumAsync(IEnumerable<ValueTask<int>> ns)
{
var sum = 0;
foreach (var nTask in ns)
{
var n = await nTask;
sum += n;
}
return sum;
}
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7#generalized-async-return-types
http://bit.ly/csasyncgeneral

var x = (f1: 1, f2: 2);
var tuple = (x.f1, x.f2, x);
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7-1#inferred-tuple-element-names
http://bit.ly/cstuplainfer

Func<string, bool> predicate = default;
int i = default;
N(default);
https://docs.microsoft.com/dotnet/csharp/programming-guide/statements-expressions-operators/default-value-expressions
http://bit.ly/csliteraldefault

(int, int) N(int[] ns = default) => default;
string O()
{
return default;
}
T P<T>()
{
T t = default;
return t;
}
https://docs.microsoft.com/dotnet/csharp/programming-guide/statements-expressions-operators/default-value-expressions
http://bit.ly/csliteraldefault

static async Task<int> Main(string[] args)
{
WriteLine("Done");
return 0;
}
https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7-1#async-main
http://bit.ly/csasyncmain

void M(int i, int j) { }
void N()
{
M(i: 2, 3);
}
https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/non-trailing-named-arguments.md
http://bit.ly/csntna

var m = 0b_101; //5
var n = 0x_00C0; // 192
https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/leading-separator.md
http://bit.ly/cs_num

class Base
{
private protected int f;
}
class DerivedInSameAssembly : Base
{
void M()
{
var x = base.f;
}
}
class DerivedInOtherAssembly : Base
{
void M()
{
var x = base.f; //error
}
}
https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/private-protected.md
http://bit.ly/csprpr

Vector Add(in Vector v1, in Vector v2)
{
v1 = default(Vector); // not OK!!
v1.X = 0; // not OK!!
Foo(ref v1.X); // not OK!!
// OK:
return new Vector(v1.X +v2.X, v1.Y + v2.Y);
}
https://docs.microsoft.com/dotnet/csharp/reference-semantics-with-value-types
http://bit.ly/csmodin

https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/readonly-ref.md#refin-extension-methods
public static Ponto Soma(in this Ponto p1, in Ponto p2) =>
new Ponto(p1.X + p2.X, p1.Y + p2.Y);
void In()
{
Ponto p1 = new Ponto(1, 2), p2 = new Ponto(3, 4);
var pResultado = p1.Soma(p2);
var pResultado2 = p1.Soma(new Ponto(3, 4));
var pResultado3 = new Ponto().Soma(new Ponto(3, 4));
}
http://bit.ly/csmodin

public static Ponto Subtrai(ref this Ponto p1, ref Ponto p2) =>
new Ponto(p1.X - p2.X, p1.Y - p2.Y);
void Ref()
{
Ponto p1 = new Ponto(1, 2), p2 = new Ponto(3, 4);
var pResultado = p1.Subtrai(ref p2);
p1.Subtrai(ref new Ponto()); // não compila
new Ponto().Subtrai(ref p1); // não compila
}
http://bit.ly/csextref

public static void Foo<T>(ref this T p1)
where T : struct
{
}
http://bit.ly/csextref

ref readonly Vector FetchOrigin() => ref origin;
void M()
{
var v1 = new Vector(1, 2, 3);
var v2 = new Vector(4, 5, 6);
var vSum = Add(v1, v2);
ref readonly var origin = ref FetchOrigin();
}
private readonly Vector origin = new Vector(0, 0, 0);
http://bit.ly/csretrefro

ref readonly var origin = ref FetchOrigin();
var origin2 = FetchOrigin(); // copy created
http://bit.ly/csretrefro

readonly struct Ponto
{
public Ponto(float x, float y)
{
X = x;
Y = y;
}
public float X { get; }
public float Y { get; }
private readonly static Ponto origem = new Ponto();
public static ref readonly Ponto Origem => ref origem;
}
https://docs.microsoft.com/dotnet/csharp/reference-semantics-with-value-types#readonly-struct-type
http://bit.ly/csrostruct

ref readonly var p = ref Ponto.Origem;
var x = p.X; // sem cópia
https://docs.microsoft.com/dotnet/csharp/reference-semantics-with-value-types#readonly-struct-type
http://bit.ly/csrostruct

ref int M()
{
var arr = new[] { 1, 2, 3 };
var otherArr = new[] { 4, 5, 6 };
ref var r = ref (arr != null ? ref arr[0]: ref
otherArr[0]);
Foo(ref (arr != null ? ref arr[0]: ref otherArr[0]));
(arr != null ? ref arr[0]: ref otherArr[0]) = 1;
return ref (arr != null ? ref arr[0]: ref otherArr[0]);
}
void Foo(ref int i) => i = 42;
https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/conditional-ref.md
http://bit.ly/csternarioref

ref struct TwoSpans<T>
{
// pode ter campos desde que não sejam classes
public Span<T> first;
public Span<T> second;
}
// erro: arrays of ref-like types are not allowed.
TwoSpans<int>[] arr = null;
https://docs.microsoft.com/en-us/dotnet/csharp/reference-semantics-with-value-types#ref-struct-type

readonly ref struct ReadOnlyRefPoint2D
{
public int X { get; }
public int Y { get; }
public ReadOnlyRefPoint2D(int x, int y) =>
(X, Y) = (x, y);
}
https://docs.microsoft.com/dotnet/csharp/reference-semantics-with-value-types#readonly-ref-struct-type

void M()
{
Span<int> arr = stackalloc int[3];
}
https://msdn.microsoft.com/en-us/magazine/mt814808.aspx
Não é unsafe

Span<int> RowFive = new Span<int>(PascalsTriangle, 10, 5);
fixed (int* ptrToRow = RowFive)
{
// Soma os números 1,4,6,4,1
var sum = 0;
for (int i = 0; i < RowFive.Length; i++)
{
sum += *(ptrToRow + i);
}
Console.WriteLine(sum);
}
https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.3/pattern-based-fixed.md
int[] PascalsTriangle = {
1,
1, 1,
1, 2, 1,
1, 3, 3, 1,
1, 4, 6, 4, 1,
1, 5, 10, 10, 5, 1 };
Span<T>.GetPinnableReference()

unsafe struct S
{
public fixed int myFixedField[10];
}
class C
{
private static S s = new S();
unsafe public void M()
{
int p = s.myFixedField[5];
}
}
https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-7-3#indexing-fixed-fields-does-not-require-pinning
// CSharp 7.2
fixed (int* ptr = s.myFixedField)
{
int p = ptr[5];
}

var structs = new StructGrande[]
{ new StructGrande(), new StructGrande() };
ref StructGrande refLocal = ref structs[0];
refLocal = ref structs[1];
https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-7-3#ref-local-variables-may-be-reassigned

unsafe void M()
{
int* pArr = stackalloc int[3] { 1, 2, 3 };
int* pArr2 = stackalloc int[] { 1, 2, 3 };
Span<int> arr = stackalloc[] { 1, 2, 3 };
}
https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-7-3#stackalloc-arrays-support-initializers

unsafe public static byte[] ToByteArray<T>
(this T argument) where T : unmanaged
{
var size = sizeof(T);
var result = new byte[size];
byte* p = (byte*)&argument;
for (var i = 0; i < size; i++)
result[i] = *p++;
return result;
}
https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters#unmanaged-constraint

public static TDelegate TypeSafeCombine<TDelegate>
(this TDelegate source, TDelegate target)
where TDelegate : System.Delegate =>
System.Delegate.Combine(source, target)
as TDelegate;
Action first = () => Console.WriteLine("this");
Action second = () => Console.WriteLine("that");
var combined = first.TypeSafeCombine(second);
combined();
https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters#delegate-constraints

public static Dictionary<int, string> EnumNamedValues<T>()
where T : System.Enum
{
var result = new Dictionary<int, string>();
var values = Enum.GetValues(typeof(T));
foreach (int item in values)
result.Add(item, Enum.GetName(typeof(T), item));
return result;
}
enum Rainbow { Red, Orange, Yellow, Green, Blue, Indigo, Violet }
var map = EnumNamedValues<Rainbow>();
foreach (var pair in map)
Console.WriteLine($"{pair.Key}:t{pair.Value}");
https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters#enum-constraints

https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.3/expression-variables-in-initializers.md
var t1 = (1, 2);
var t2 = (3, 4);
var iguais = t1 == t2;
var diferentes = t1 != t2;

var query = from text in strings
select int.TryParse(text, out int value)
? value : (int?)null;

public class Foo
{
protected Foo(out int i) => i = 1;
}
public class Bar : Foo
{
public int Value { get; }
public Bar() : base(out int value) => Value = value;
}

public class Baz
{
private readonly int field1 =
int.TryParse(SomeStatic.Text, out int value)
? Value
: -1;
}

https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.3/auto-prop-field-attrs.md
[Serializable]
public class Foo
{
[field: NonSerialized]
public string MySecret { get; set; }
}

public class Cartesian { public int X { get; } public int Y { get; } }
public class Polar
{
public static bool operator is(Cartesian c, out double R, out double Theta)
{
R = Math.Sqrt(c.X * c.X + c.Y * c.Y);
Theta = Math.Atan2(c.Y, c.X);
return c.X != 0 || c.Y != 0;
}
}
void M()
{
var c = new Cartesian(3, 4);
if (c is Polar(var R, _)) WriteLine(R);
}
https://github.com/dotnet/csharplang/blob/master/proposals/patterns.md

void N(string? aNullableString, bool condition) {
WriteLine(aNullableString.Length); // warning
if (aNullableString != null)
WriteLine(aNullableString); // no warning
if (!string.IsNullOrWhiteSpace(aNullableString))
WriteLine(aNullableString!.Length); // I know better
var anotherNullableString = condition ? "Hello" : aNullableString;
WriteLine(anotherNullableString.Length); // warning
var yetAnotherNullableString = condition ? "Hello" : null;
WriteLine(yetAnotherNullableString.Length); // warning
string nonNullableString = null; //warning
WriteLine(nonNullableString); // no warning
}
https://github.com/dotnet/csharplang/blob/master/proposals/nullable-reference-types.md
https://github.com/dotnet/roslyn/blob/features/NullableReferenceTypes/docs/features/NullableReferenceTypes/README.md

async Task M()
{
foreach await (var i in GetStream())
WriteLine(i);
}
IAsyncEnumerable<int> GetStream() => new[] { 1, 2, 3 }.ToAsyncEnumerable();
async IAsyncEnumerable<int> MyIterator()
{
for (int i = 0; i < 100; i++)
{
yield return i;
}
}
https://github.com/dotnet/csharplang/blob/master/proposals/async-streams.md

using await (IAsyncDisposable resource = await store.GetRecordAsync(…)) { … }
class Foo : IAsyncDisposable
{
public async Task DisposeAsync()
{
await ...
}
}
https://github.com/dotnet/csharplang/blob/master/proposals/async-streams.md

interface I
{
void M() { WriteLine("I.M"); }
}
class C : I { } // OK
void M()
{ I i = new C();
i.M(); // prints "I.M"
}
https://github.com/dotnet/csharplang/blob/master/proposals/default-interface-methods.md

Dictionary<string, List<int>> field =
new() { { "item1", new() { 1, 2, 3 } } };
XmlReader.Create(reader,
new() { IgnoreWhitespace = true });
https://github.com/dotnet/csharplang/blob/master/proposals/target-typed-new.md

// list[Index.CreateFromEnd(1)]
var ultimoItem = list[^1];
// list[Index.CreateFromEnd(2)]
var penultimoItem = list[^2];
// list[3, Index.CreateFromEnd(2)]
var multiDimensional = list[3, ^2];
https://github.com/dotnet/csharplang/blob/master/proposals/ranges.md

// list[Range.Create(2, Index.CreateFromEnd(3))]
var slice1 = list[2..^3];
// list[Range.ToEnd(Index.CreateFromEnd(3))]
var slice2 = list[..^3];
// list[Range.FromStart(2)]
var slice3 = list[2..];
// list[Range.All]
var slice4 = list[..];
// list[Range.Create(1, 2), Range.All]
var multiDimensional = list[1..2, ..]
https://github.com/dotnet/csharplang/blob/master/proposals/ranges.md

class Person : IEquatable<Person>
{
public string First { get; }
public string Last { get; }
public Person(string First, string Last) => (this.First, this.Last) = (First, Last);
public void Deconstruct(out string First, out string Last)
=> (First, Last) = (this.First, this.Last);
public bool Equals(Person other)
=> other != null && First == other.First && Last == other.Last;
public override bool Equals(object obj) => obj is Person other ? Equals(other) : false;
public override int GetHashCode() => GreatHashFunction(First, Last);
…
}
class Person(string First, string Last);
https://github.com/dotnet/csharplang/blob/master/proposals/records.md

extension class Enrollee extends Person
{
// static field
static Dictionary<Person, Professor> enrollees = new Dictionary<Person, Professor>();
// instance method
public void Enroll(Professor supervisor) { enrollees[this] = supervisor; }
// instance property
public Professor Supervisor => enrollees.TryGetValue(this, out var supervisor) ? supervisor : null;
// static property
public static ICollection<Person> Students => enrollees.Keys;
// instance constructor
public Person(string name, Professor supervisor) : this(name) { this.Enroll(supervisor); }
}
https://github.com/dotnet/csharplang/issues/192

public shape SGroup<T>
{
static T operator +(T t1, T t2);
static T Zero { get; }
}

public static AddAll<T>(T[] ts) where T : SGroup<T>
{
var result = T.Zero;
foreach (var t in ts) { result += t; }
return result;
}

w w w. l a m b d a 3 . c o m . b r
Obrigado!
Giovanni Bassi
@giovannibassi
/giggio.tech

TDC2018SP | Trilha .Net - Novidades do C# 7 e 8

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