using statement

Learn automatic dispose with the using statement and using declaration.

The using statement and declaration

The using statement automatically Disposes an IDisposable object at the end of a block. using (var r = new Reader()) { /* ... */ } calls r.Dispose() when the block ends, even on exception.

Since C# 8 the using declaration is shorter: using var r = new Reader(); disposes r when its scope ends. Both forms do the same job.

The classic using statement

The classic form of the using statement uses parens and a block: using (var r = new Reader()) { /* use r */ }. When the block ends (normally or via exception) Dispose is called.

Multiple resources require nested usings. Modern code prefers the using declaration; it is cleaner when no block is needed.

Exercise Use a using declaration with Reader

The Reader class implements IDisposable. In public void Dispose() write Console.WriteLine("Closed");. In Main use using var r = new Reader();.

Show example solution

using var r = new Reader();
Example solution:
using System;

class Reader : IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("Closed");
    }
}

class Program
{
    static void Main()
    {
        using var r = new Reader();
    }
}

Test yourself

When does a using declaration call Dispose?
- When the object is created
- Only at Main exit
- When the GC runs
- When the scope ends
Show answer

When the scope ends — Correct. A using declaration disposes at scope end.

Complete the using declaration

using ____ r = new Reader();

Show answer

using var r = new Reader();

Match the using forms

using var r;

Declaration
using (var r = ...)

Statement
Dispose()

Frees the resource
IDisposable

Required interface for using

Next lesson: GC.Collect

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