Csharp 8
De Banane Atomic
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Switch expression
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string myVar;
switch (i)
{
case 1:
myVar = "One";
break;
case 2:
case 3:
myVar = "Two-Three";
break;
case var x when x > 0 && x < 10:
myVar = "Zero-Ten";
break;
default:
throw new ArgumentOutOfRangeException(nameof(i));
}
var myVar = i switch
{
1 => "One",
2 or 3 => "Two-Three",
> 0 and < 10 => "Zero-Ten",
_ => throw new ArgumentOutOfRangeException(nameof(i))
};
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Using declaration
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using (var file = new StreamWriter("MyFile.txt"))
{
// some code
} // file is disposed here
void MyMethod()
{
using var file = new StreamWriter("MyFile.txt");
// some code
// file is disposed here, at the end of the enclosing scope
}
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Static local function
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int x = 5; int y = 7; return Add(x, y); // Can be static because it doesn't access any variables in the enclosing scope static int Add(int left, int right) => left + right; |
Asynchronous streams / async yield
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public static async IAsyncEnumerable<int> GenerateSequence()
{
for (int i = 0; i < 20; i++)
{
await Task.Delay(100);
yield return i;
}
}
await foreach (var number in GenerateSequence())
{
Console.WriteLine(number);
}
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Indices and ranges
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var latest = myList[^1]; var secondToFour = myList[2..5]; var lastTwo = myList[^2..^0]; var firstThree = myList[..4]; var allExceptFirst = myList[2..]; |
Null-coalescing assignment / ?? =
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int? i = null; i = i == null ? 20 : i; i = i ?? 20; i ??= 20; // assign 20 to i if i is null |
Nullable reference type
| MyProject.csproj |
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>netcoreapp3.1</TargetFramework>
<!-- add this line to enable it -->
<Nullable>enable</Nullable>
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Now by default everything is non nullable. If you want to declare a type as accepting null values, you need to add ? after the type.
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string s1 = null; // Warning: Converting null literal or possible null value to non-nullable type.
string? s2 = null; // ok
// null-forgiving operator
Console.WriteLine(s2!.Length); // in this case we know that s2 is not null, so we can use "!" to instruct the compiler "s2" is not null here
// allow null even if the type is not nullable
public void MyMethod([AllowNull]ref string value)
{ }
// disallow null even if the type is nullable
public void MyMethod([DisallowNull]ref string? value)
{ }
private string s1 = "";
// allow null for setter even if the type is not nullable
[AllowNull]
public string S1
{
get => s1;
set => s1 = value ?? "";
}
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.NET Framework
The C# 8 / .NET Framework combination is not officially supported by Microsoft.
It can be forced by editing the csproj file.
| MyProject.csproj |
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<TargetFrameworkVersion>v4.7.2</TargetFrameworkVersion>
<LangVersion>8.0</LangVersion>
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- default interface members won't work
- asynchronous streams and indices and ranges will need polyfill nuget package
