c# using 语句是否需要赋值？

Question

起初我有这样的代码：

WindowsIdentity otherIdentity = // got that from somewhere else
WindowsImpersonationContext context = otherIdentity.Impersonate();
Ldap.DoStuff();
context.Undo();
context.Dispose();

知道 WindowsImpersonationContext 实现 IDisposable 并且 Dispose() 也调用 Undo()，我想我应该改用 using：

using (var context = otherIdentity.Impersonate())
{
    // Run as other user
    Ldap.DoStuff();
}

现在，ReSharper 正确地注意到我没有使用 context 并建议删除分配。这也有效吗？它在编译时扩展到什么代码？

using (otherIdentity.Impersonate())
{
    Ldap.DoStuff();
}

Answer 1

是的，你可以在using语句中省略变量，编译器会自动引入一个隐藏变量，就好像你写了

using (var temp = otherIdentity.Impersonate())
{
    Ldap.DoStuff();
}

除了您不能在 using 语句的正文中访问 temp。

奇怪的是，MSDN Library 中似乎没有记录此语法。相反，请参考 C# 规范：

A using statement of the form
using (ResourceType resource = expression) statement
corresponds to one of three possible expansions.

[...]

A using statement of the form
using (expression) statement
has the same three possible expansions. In this case ResourceType is implicitly the compile-time type of the expression, if it has one. Otherwise the interface IDisposable itself is used as the ResourceType. The resource variable is inaccessible in, and invisible to, the embedded statement.

c# using 语句是否需要赋值？

Does c# using statement need assignment?

c#

using-statement