C# 6.0 11個新特性

1. 靜態using(static using)

靜態using聲明允許不使用類名直接調用靜態方法。

The static using declaration allows invoking static methods without the class
name.

In C# 5

using System;

Console.WriteLine("Hello, World!");

In C# 6

using static System.Console;

WriteLine("Hello, World");

2. 表達式方法(Expression-Bodied Methods)

使用表達式方法，只有一條語句的方法可以使用lambda語法寫。

With expression-bodied methods, a method that includes just one statement can
be written with the lambda syntax.

In C# 5

public bool IsSquare(Rectangle rect)
{
    return rect.Height == rect.Width;
}

In C# 6

public bool IsSquare(Rectangle rect) => rect.Height == rect.Width;

3. 表達式屬性(Expression-Bodied Properties)

跟表達式方法類似，只有一個get訪問器的單行屬性可以使用lambda語法寫。

Similar to expression-bodied methods, one-line properties with only a get accessor
can be written with the lambda syntax

In C# 5

public string FullName
{
    get
    {
        return FirstName +"" + LastName;
    }
}

In C# 6

public string FullName => FirstName +"" + LastName;

4. 自動屬性初始化器(Auto-Implemented Property Intializers)

自動屬性可以使用屬性初始化器初始化。

Auto-implemented properties can be initialized with a property initializer.

In C# 5

public class Person
{
    public Person()
    {
        Age = 24;
    }
    public int Age {get; set;}
}

In C# 6

public class Person
{
    public int Age {get; set;} = 42;
}

5. 只讀自動屬性(Read-Only Auto Properties)

C# 5需要完整的屬性語法實現只讀屬性，C# 6可以使用自動屬性實現。

To implement read-only properties, C# 5 requires the full property syntax. With
C# 6, you can do this using auto-implemented properties.

In C# 5

private readonly int _bookId;
public BookId
{
    get
    {
        return _bookId;
    }
}

In C# 6

public BookId {get;}

6. nameof操作符(nameof Operator)

欄位、屬性、方法和類型的name可以通過nameof訪問。使用nameof，可以方便的重構name變化。

With the new nameof operator, names of fields, properties, methods, or types can
be accessed. With this, name changes are not missed with refactoring.

In C# 5

public void Method(object o)
{
    if (o == null) throw new ArgumentNullException("o");

In C# 6

public void Method(object o)
{
    if (o == null) throw new ArgumentNullException(nameof(o));

7. Null傳遞操作符(Null Propagation Operator)

Null傳遞操作符簡化了空值檢查。

The null propagation operator simplifies null checks.

In C# 5

int? age = p == null ? null : p.Age;

var handler = Event;
if (handler != null)
{
    handler(source, e);
}

In C# 6

int? age = p?.Age;

handler?.Invoke(source, e);

8. 字元串插值(String Interpolation)

字元串差值移除了對string.Format的調用，使用表達式占位符取代數字格式占位符。

The string interpolation removes calls to string.Format. Instead of using
numbered format placeholders in the string, the placeholders can include
expressions.

In C# 5

public override ToString()
{
    return string.Format("{0}, {1}", Title, Publisher);
}

In C# 6

public override ToString() => $"{Title} {Publisher}";

9. 字典初始化器(Dictionary Initializers)

字典可以使用類似集合的字典初始化器初始化。

Dictionaries can now be initialized with a dictionary initializer—similar to the
collection initializer.

In C# 5

var dict = new Dictionary<int, string>();
dict.Add(3,"three");
dict.Add(7,"seven");

In C# 6

var dict = new Dictionary<int, string>()
{
    [3] ="three",
    [7] ="seven"
};

10. 異常過濾器(Exception Filters)

異常過濾器允許你在捕獲異常前進行過濾。

Exception filters allow you to filter exceptions before catching them.

In C# 5

try
{
    //etc.
} catch (MyException ex)
{
    if (ex.ErrorCode != 405) throw;
    // etc.
}

In C# 6

try
{
    //etc.
} catch (MyException ex) when (ex.ErrorCode == 405)
{
    // etc.
}

11. 在Catch使用Await(Await in Catch)

await可以在catch塊中直接使用，C# 5中需要變通使用。

await can now be used in the catch clause. C# 5 required a workaround.

In C# 5

bool hasError = false;
string errorMessage = null;
try
{
    //etc.
} catch (MyException ex)
{
    hasError = true;
    errorMessage = ex.Message;
} 
if (hasError)
{
    await new MessageDialog().ShowAsync(errorMessage);
}

In C# 6

try
{
    //etc.
} catch (MyException ex)
{
    await new MessageDialog().ShowAsync(ex.Message);
}