C# Language Using Statement Multiple using statements with one block
Example
It is possible to use multiple nested using statements without added multiple levels of nested braces. For example:
using (var input = File.OpenRead("input.txt"))
{
using (var output = File.OpenWrite("output.txt"))
{
input.CopyTo(output);
} // output is disposed here
} // input is disposed here
An alternative is to write:
using (var input = File.OpenRead("input.txt"))
using (var output = File.OpenWrite("output.txt"))
{
input.CopyTo(output);
} // output and then input are disposed here
Which is exactly equivalent to the first example.
Note: Nested using statements might trigger Microsoft Code Analysis rule CS2002 (see this answer for clarification) and generate a warning. As explained in the linked answer, it is generally safe to nest using statements.
When the types within the using statement are of the same type you can comma-delimit them and specify the type only once (though this is uncommon):
using (FileStream file = File.Open("MyFile.txt"), file2 = File.Open("MyFile2.txt"))
{
}
This can also be used when the types have a shared hierarchy:
using (Stream file = File.Open("MyFile.txt"), data = new MemoryStream())
{
}
The var keyword cannot be used in the above example. A compilation error would occur. Even the comma separated declaration won't work when the declared variables have types from different hierarchies.
