What is the C# Using block and why should I use it? [duplicate]

Question

What is the purpose of the Using block in C#? How is it different from a local variable?

Answer 1

If the type implements IDisposable, it automatically disposes that type.

Given:

public class SomeDisposableType : IDisposable {    ...implmentation details... } 

These are equivalent:

SomeDisposableType t = new SomeDisposableType(); try {     OperateOnType(t); } finally {     if (t != null) {         ((IDisposable)t).Dispose();     } } 

using (SomeDisposableType u = new SomeDisposableType()) {     OperateOnType(u); } 

The second is easier to read and maintain.

---

Since C# 8 there is a new syntax for using that may make for more readable code:

using var x = new SomeDisposableType(); 

It doesn't have a { } block of its own and the scope of the using is from the point of declaration to the end of the block it is declared in. It means you can avoid stuff like:

string x = null; using(var someReader = ...) {   x = someReader.Read(); } 

And have this:

using var someReader = ...; string x = someReader.Read(); 

Answer 2

Using calls Dispose() after the using-block is left, even if the code throws an exception.

So you usually use using for classes that require cleaning up after them, like IO.

So, this using block:

using (MyClass mine = new MyClass()) {   mine.Action(); } 

would do the same as:

MyClass mine = new MyClass(); try {   mine.Action(); } finally {   if (mine != null)     mine.Dispose(); } 

Using using is way shorter and easier to read.