C# 程式設計/關鍵字/using

在 C# 中，using 關鍵字有兩個完全不相關的含義，取決於它是用作指令還是語句。

指令

using 作為指令解析無限定型別引用，這樣開發者就不必指定完整的名稱空間。

例子

using System;
 
// A developer can now type ''Console.WriteLine();'' rather than ''System.Console.WriteLine()''.

using 還可以為引用型別提供命名空間別名。

例子

using utils = Company.Application.Utilities;

語句

using 作為語句會自動呼叫指定物件的 dispose。 該物件必須實現 IDisposable 介面。只要它們是相同型別，就可以在一個語句中使用多個物件。

例子

using (System.IO.StreamReader reader = new StreamReader("readme.txt"))
{
    // read from the file
}
 
// The file readme.txt has now been closed automatically.

using (Font headerFont = new Font("Arial", 12.0f),
            textFont = new Font("Times New Roman", 10.0f))
{
    // Use headerFont and textFont.
}

// Both font objects are closed now.

C# 關鍵字
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C# 特殊識別符號（上下文關鍵字）
add alias async await dynamic get global nameof partial remove set value when where yield
上下文關鍵字（用於查詢）
ascending by descending equals from group in into join let on orderby select where