此文档介绍了 C# 10 的新特性，包括命名空间、扩展属性模式、结构、Lambda 表达式、字符串插补和调用方参数表达式。文中还提供了示例代码和编程技巧，强调了使用这些特性的注意事项与最佳实践。课程强调尊重知识产权，所有内容仅供课程学习使用。

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Bill Chung
C# 10

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about me
• Bill Chung
• 專長是說故事
• 海角點部落
https://dotblogs.com.tw/billchung
• github https://github.com/billchungiii
請尊重講師的著作權及智慧財產權!
此課程之教材、程式碼等、僅供課程中學習用、請不要任意自行散佈、重製、分享，謝謝
https://mvc.tw

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大綱
• Name Space
• Extended property patterns
• Structure
• Lambda
• String
• Caller Argument Expression
https://mvc.tw

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Name Space

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• 一次設定，專案全域引入
• global using [namespace]
global usings

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• .NET６
• 編譯器會自動引入基本的命名空間
• 檔案藏在 obj 目錄下 [project name].GlobalUsings.g.cs
implicit usings

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<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net6.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
<ItemGroup>
<Using Include="System.Reflection" />
</ItemGroup>
</Project>

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file-scoped namespace
namespace ConsoleApp1;
internal class Class1 { }
namespace ConsoleApp1
{
internal class Class1 { }
}

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Extended
Property
Patterns

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extended property patterns
if (p is (string firstName, "Chung", _) { Address: { City: string city, ZipCode: "100" } })
if (p is (string firstName, "Chung", _) { Address.City: string city, Address.ZipCode: "100" })

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Structure

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parameterless constructors
struct MyStructure
{
public double Value { get; init; }
public string Name { get; init; }
public MyStructure()
{
Value = double.NaN;
Name = string.Empty;
}
public MyStructure(int value, string name)
{
Value = value;
Name = name;
}
public override string ToString()
{
return $"{Value},{Name}";
}
}

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• 回傳 field / property 型別的預設值，而非初始化設定的值。
default value expressions

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filed / property initializer
struct MyStructure
{
public double Value { get; set; }
public string Name { get; set; } = "Bill";

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record strcutrue
public readonly record struct Point(double X, double Y, double Z);
public readonly record struct Point
{
public double X { get; init; }
public double Y { get; init; }
public double Z { get; init; }
}

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• 過去：with 敘述僅能用在 record
• 現在：可以用在 structure 和 anonymous type
with expression
var s1 = new MyStructure();
var s3 = s1 with { Name = "ABC", Value = 100.0 };

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Lambda

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Infer delegate type
var parse1 = (string s) => int.Parse(s);
object parse2 = (string s) => int.Parse(s);
Delegate parse3 = (string s) => int.Parse(s);
var read = Console.Read;
LambdaExpression parseExpr = (string s) => int.Parse(s);
Expression parseExpr = (string s) => int.Parse(s);

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Declared return type
var choose = object(bool b) => b? 1 : "two";

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Attributes
Func<string, int> parse =[Some(1)] (s) => int.Parse(s);

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String

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• 字串常數可使用字串插值功能，但必須都是常數
String Constant
const string Name = "Bill";
const string ProgramName = $"{Name} program";

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• 字串插補可以自定義處理常式
• 自訂處理常式需求
• 套用 InterpolatedStringHandlerAttribute
• 建構式需要兩個 int 型別參數 -- literalLength and formatCount
• public void AppendLiteral(string s) method
• public void AppendFormatted<T>(T t) method
Interpolated string handlers

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Caller
Argument
Expression

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• 無需使用反射就能得到呼叫端引數的表達式字串
CallerArgumentExpressionAttribute
public static void CheckExpression(bool condition, [CallerArgumentExpression("condition")] string? message = null)
{
Console.WriteLine($"Condition: {message}");
}
public static void CheckDelegate(Func<int, int, int> func, [CallerArgumentExpression("func")] string? message = null)
{
Console.WriteLine($"Func is : {message}");
}
public static void CheckSquence(IEnumerable<int> source, [CallerArgumentExpression("source")] string? message = null)
{
Console.WriteLine($"Squence is : {message}");
}

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The END
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