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The using statement obtains one or more resources, executes a statement, and then disposes of the resource.
using ( resource-acquisition ) embedded-statement
A resource is a class or struct that implements System.IDisposable, which includes a single parameterless method named Dispose. Code that is using a resource can call Dispose to indicate that the resource is no longer needed. If Dispose is not called, then automatic disposal eventually occurs as a consequence of garbage collection.
If the form of resource-acquisition is local-variable-declaration then the type of the local-variable-declaration must be System.IDisposable or a type that can be implicitly converted to System.IDisposable. If the form of resource-acquisition is expression then this expression must be System.IDisposable or a type that can be implicitly converted to System.IDisposable.
Local variables declared in a resource-acquisition are read-only, and must include an initializer.
A using statement is translated into three parts: acquisition, usage, and disposal. Usage of the resource is implicitly enclosed in a try statement that includes a finally clause. This finally clause disposes of the resource. If a null resource is acquired, then no call to Dispose is made, and no exception is thrown.
For example, a using statement of the form
using (R r1 = new R ())
is precisely equivalent to
R r1 =
A resource-acquisition may acquire multiple resources of a given type. This is equivalent to nested using statements. For example, a using statement of the form
using (R r1 = new R(), r2 = new R())
is precisely equivalent to:
r1 = new R())
using (R r2 = new R())
which is, by expansion, precisely equivalent to:
R r1 =
R r2 = new R();
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