Resource Lifetime in

About Resource Lifetime

resource-cleanup uses the IDispose interface to signal to callers of a class that there are resources or program state that need releasing or resetting in a timely fashion when the object in question is no longer required. In this exercise we have introduced some syntactic sugar, with the using keyword, that makes the code less verbose and less likely that significant calls will be omitted.

using can be seen as replacing try/finally for some use cases.

File file = null;
try
{
    file = new File("myStuff.txt");
    file.Write("more stuff");
}
finally
{
    file.Dispose();
}

This syntax is replaced with the more compact and foolproof:

using (var file = new File("myStuff.txt")
{
    file.Write("more stuff");
}

Note that multiple resources can be conveniently combined following standard rules for single line blocks:

using (var file = new File("mystuff.txt")
using (var fileWriter = new StreamWriter(file)
{
     ...
}

In C# 8 the following variation has been introduced where the using statement comes at the start of a block:

using var file = new File("myStuff.txt");
file.Write("more stuff");

This allows you to have multiple disposable objects in the same block and to more naturally handle try/catch:

using var fileIn = new File("myStuff.txt");
using var fileOut = new File("yourStuff.txt");
try
{
    var stuff = fileIn.Read();
    fileOut.Write(stuff);
}
catch (Exception)
{
    LogStuff();
}

The rules related to how the using keyword can be used and with instances of what sort of types are detailed here.

Note for Java Developers

Java developers may recognize this as an analog of the automatic resource management mechanism introduced in Java 7. They are very similar. Java's syntax, which repurposes try has the advantage of incorporating catch blocks more naturally than does C#'s using.

Versions

Note that the more flexible version of using where it does not have its own syntactic block was introduced in C# 8 so you may need to check if the code base you are working on is using C# 8 or later.

Reference

using statement documentation describes how and when to use the using keyword.