C# using

我们知道 using 语句只不过是提供能确保正确使用 IDisposable 对象的方便语法。

1:  using (IDisposable reader1 = new StreamReader(inputFileName1),
2:                     reader2 = new StreamReader(inputFileName2),
3:                     writer = new StreamWriter(outputFileName))
4:  {
5:    Merge(reader1 as TextReader, reader2 as TextReader, writer as TextWriter);
6:  }

using (R r1 = new R()) { 
r1.F(); 
} 
完全等效于 

R r1 = new R(); 
try { 
r1.F(); 
} 
finally { 
if (r1 != null) ((IDisposable)r1).Dispose(); 
}