G8甚至还没有发布RTM，我已经在写有关它的文章。 怎么了 好吧，主要的想法是，被警告的人是武装的。 因此，在本篇文章中，将介绍当前已知的内容，如果全部都是设置，那么正确。
可空引用类型
, , «» . — , NULL nullptr ++. — zero-terminated strings, (n). null.
C# , :
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string MiddleName { get; set; }
public Person(string first, string last, string middle) =>
(FirstName, LastName, MiddleName) = (first, last, middle);
public string FullName =>
$"{FirstName} {MiddleName[0]} {LastName}";
}
. , , . C# null. ($ string.Format()), . null-, NRE (NullReferenceException).
, .. null, 100500 . Optional , , .
- , . (NuGet JetBrains.Annotations) :
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
[CanBeNull] public string MiddleName { get; set; }
public Person(string first, string last, [CanBeNull] string middle) =>
(FirstName, LastName, MiddleName) = (first, last, middle);
public string FullName =>
$"{FirstName} {MiddleName[0]} {LastName}";
}
NRE MiddleName[0].
Microsoft… , . , VS . . .
, . , . , C#8 :
#nullable enable
. , -
var p = new Person("Dmitri", "Nesteruk", null);
warning:
1>NullableReferenceTypes.cs(26,48,26,52): warning CS8625: Cannot convert null literal to non-nullable reference or unconstrained type parameter.
-, , ( treat warnings as errors ).
, ? - - C#, MiddleName null [0] .
:
public string? MiddleName;
, ? - string? Nullable<T>, , T : struct, - . — , .. string.
. - , :
public string FullName => $"{FirstName} {MiddleName?[0]} {LastName}";
: IL? — ! : nullable nullable [Nullable]. : .
C#8 - -. , nullable-
string? s = GetString();
warning. :
if (s != null){ char c = s[0];}
! , . .
null. — «», , null- .
— . :
(null as Person).FullName warning
(null as Person)!.FullName warning , ..
(null as Person)!!!!!!!!!!!!!.FullName
(null as Person)!?.FullName null; , ?!,
, - BCL .
Type t = Type.GetType("abracadabra");Console.WriteLine(t.Name);
. - Type.GetType() null , BCL nullable , .
, «»
Type t = Type.GetType("abracadabra");
Type? u = t;
Console.WriteLine(u.Name);
. , t != null, u null, .
Nullable reference types — , . . , , - nullability , , .
: , , , . , X~N(0,1), E[X²] V[X²]?
, , « ».
, : Index Range.
Index
, int uint? : ( ). , C# x[-1] .
. .. -1 , , .
C# . , . , Index , :
Index i0 = 2; // implicit conversion
, , .
Index ( — ):
:
Index i1 = new Index(0, false);
, , . ( , ) :
var i2 = ^0; // Index(0, true)
! , ^ ( , LaTeX, ), « ».
, , (operator this[]) Index,
var items = new[] { 1, 2, 3, 4, 5 };
items[^2] = 33; // 1, 2, 33, 4, 5
Range
— Range, , , 1. :
X..Y
« X Y». , Y — Y. .
, :
var a = i1..i2; // Range(i1, i2) —
var b = i1..; // Range(i1, new Index(0, true)); — i1
var c = ..i2; // Range(new Index(0, false), i2) — i2
var e = ..; — ,
Range.ToEnd(2); — — , ; , dotPeek, ilSpy
?
, ++ (undefined behavior?). , Range C# . : « ».
x = {1, 2, 3}. x[0..2] {1, 2}, x[..2] x[..], {1, 2, 3}.
.. x[2] x[^1] — , Range- !
-, X..Y X <= Y ( ?). ( 7..3), ArgumentOutOfRangeException. .. , .
-, «» , 1..2..100 . . MATLAB.
Range :
, Index/Range operator this[]. , « » . , (singly linked list), - « » — .
, struct-. - , «» , .
, :
Default Interface Members
, . , — ?
. Enumerable.Count() — while (x.MoveNext()) , . Count() :
if (x is IList<T> list)
return list.Count;
? IReadOnlyList<T>, ? « »?!?
, , open-closed principle SOLID, .. — .
? , , , - Count(), IReadOnlyList<T>, , . ! - IReadOnlyList<T>.Count() IEnumerable<T>.Count()? , ! .
. , - -, .
:
public interface IHuman
{
string Name { get; set; }
public void SayHello()
{
Console.WriteLine($"Hello, I am {Name}");
}
}
public class Human : IHuman
{
public string Name { get;set; }
}
, , :
Human human = new Human() { Name = "John" };
human.SayHello(); // will not compile
? , . — , , , .
, ? , , , . Human SayHello()? , .
: , :
IHuman human = new Human() { Name = "John" };
human.SayHello();
((IHuman)new Human { … }).SayHello();
, , : Foo() ( ), Foo(), :
public interface IHuman
{
string Name { get; set; }
void SayHello()
{
Console.WriteLine($"Hello, I am {Name}");
}
}
public interface IFriendlyHuman : IHuman
{
void SayHello()
{
Console.WriteLine( $"Greeting, my name is {Name}");
}
}
((IHuman)new Human()).SayHello();
// Hello, I am John
((IFriendlyHuman)new Human()).SayHello();
// Greeting, my name is John
, IFriendlyHuman.SayHello() override- IHuman.SayHello(), ! SayHello() ? :
public interface IFriendlyHuman : IHuman
{
void IHuman.SayHello()
// ↑↑↑↑↑↑
{
Console.WriteLine( $"Greeting, my name is {Name}");
}
}
SayHello() , IHuman IFriendlyHuman , :
((IHuman)new Human()).SayHello();
Greeting, my name is John
((IFriendlyHuman)new Human()).SayHello();
Greeting, my name is John
Diamond Inheritance
, « override-» - , :
interface ITalk { void Greet(); }
interface IAmBritish : ITalk
{
void ITalk.Greet() => WriteLine("Good day!");
}
interface IAmAmerican : ITalk
{
void ITalk.Greet() => WriteLine("Howdy!");
}
class DualNational : IAmBritish, IAmAmerican {}
// Error CS8705 Interface member 'ITalk.Greet()' does not have a most specific implementation. Neither 'IAmBritish.ITalk.Greet()', nor 'IAmAmerican.ITalk.Greet()' are most specific.
, « » ( , ) , , - - IAmAmerican.Greet() — , -, ?
. , , , API. — -. -?
Pattern Matching
F# . — F# , , # , .
, F# match # switch. C#8 .
Property Matching
, :
struct PhoneNumber{
public int Code, Number;
}
var phoneNumber = new PhoneNumber();
var origin = phoneNumber switch {
{ Number: 112 } => "Emergency",
{ Code: 44 } => "UK"
};
phoneNumber, . switch statement switch expression, - .
, — , . : default-init ( , default(T) ) . , , :
:
, , :
var origin = phoneNumber switch {
{ Number: 112 } => "Emergency",
{ Code: 44 } => "UK",
{ } => "Indeterminate",
_ => "Missing"
};
? , 2 : _ (), , {} null.
, . ?
var origin = phoneNumber switch {
{ Number: 112 } => "Emergency",
{ Code: 44 } => "UK",
{ } => "Unknown"
};
? phoneNumber struct — , class. - , null, … nullable reference types!
, .
- , . nullable reference types — , nullable , recursive patterns — .
F#, , . C# , , , C# — .
, « » C# -, :
var personsOrigin = person switch {
{ Name: "Dmitri" } => "Russia",
{ PhoneNumber: { Code: 46 } } => "Sweden",
{ Name: var name } => $"No idea where {name} lives"
};
. — , person.PhoneNumber Code 46. — . , «».
: switch-. :
var error = person switch {
null => "Object missing",
{ PhoneNumber: null } => "Phone number missing entirely",
{ PhoneNumber: { Number: 0 } } => "Actual number missing",
{ PhoneNumber: { Code: var code } } when code < 0 => "WTF?",
{ } => null // no error
};
if (error != null)
throw new ArgumentException(error);
, : , when , .
- «» . , :
IEnumerable<int> GetMainOfficeNumbers()
{
foreach (var pn in numbers)
{
if (pn is ExtendedPhoneNumber { Office: "main" })
yield return pn.Number;
}
}
, , . .
— , , . Deconstruct() out-.
, - :
var type = shape switch
{
Rectangle((0, 0), 0, 0) => "Point at origin",
Circle((0, 0), _) => "Circle at origin",
Rectangle(_, var w, var h) when w == h => "Square",
Rectangle((var x, var y), var w, var h) =>
$"A {w}×{h} rectangle at ({x},{y})",
_ => "something else"
};
, : -, , . «» — , . (_) , .
, . .
, ? , , -. . . , VS 2019 Preview (-, preview RTM), .NET Core 3 ( .NET Framework), dotPeek , .
. () . ■