Exception Handling in C# - Using Statements

(Page 6 of 8 )

In C#, the nearest you can get to the "ideal" version is this:


private static char[] ReadSource(string filename)
{
    FileInfo file = new FileInfo(filename);
    int length = (int)file.Length;
    char[] source = new char[length];
    using (TextReader reader = file.OpenText())
    {
        reader.Read(source, 0, length);
    }
    return source;
}



This is pretty close. And as I'll explain shortly it has a number of features that improve on the "ideal" version. But first let's look under the lid to see how it actually works.

Using Statement Translation

The C# ECMA specification states that a using statement:


using (type variable = initialization)
    embeddedStatement
is exactly equivalent to: 
{
    type variable = initialization;
    try
    {
        embeddedStatement
    }
    finally
    {
        if (variable != null) 
        {
            ((IDisposable)variable).Dispose();
        }
    }
}



This relies on the IDisposable interface from the System namespace:


namespace System
{
    public interface IDisposable
    {
        void Dispose();
    }
}



Note that the cast inside the finally block implies that variable must be of a type that supports the IDisposable interface (either via inheritance or conversion operator). If it doesn't you'll get a compile time error.

Using TextReader Translation

Not surprisingly, TextReader supports the Disposable interface and implements Dispose to call Close. This means that this:


using (TextReader reader = file.OpenText())
{ 
    reader.Read(source, 0, length);
}



is translated, under the hood, into this:


{
    TextReader reader = file.OpenText();
    try
    {
        reader.Read(source, 0, length);
    }
    finally
    {
        if (reader != null)
        {
            ((IDisposable)reader).Dispose();
        }
    }
}



Apart from the cast to IDisposable this is identical to the best general Java solution. The cast is required because this is a general solution.

Next: Do it Yourself? >>
 

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