Real-world examples where C# 'out' parameters are useful?

Question

I\'m reading up on core C# programming constructs and having a hard time wrapping my head around the out parameter modifier. I know what it does by reading but

Answer 1

As others have said - out parameters allow us to return more than one value from a method call without having to wrap the results in struct/class.

The addition of the xxx.TryParse methods greatly simplified the coding necessary to convert between a string value (frequently from the UI) and a primitive type.

An example of what you might have had to write to achieve the same functionality is here:

/// 

/// Example code for how  might be implemented.
/// 
/// A string to convert to an integer.
/// The result of the parse if the operation was successful.
/// true if the  parameter was successfully 
/// parsed into the  integer; false otherwise.
public bool TryParse(string integerString, out int result)
{
    try
    {
        result = int.Parse(integerString);
        return true;
    }
    catch (OverflowException)
    {
        // Handle a number that was correctly formatted but 
        // too large to fit into an Int32.
    }
    catch (FormatException)
    {
        // Handle a number that was incorrectly formatted 
        // and so could not be converted to an Int32.
    }

    result = 0; // Default.
    return false;
}

The two exception checks that are avoided here make the calling code much more readable. I believe that the actual .NET implementations avoid the exceptions altogether so perform better as well. Similarly, this example shows how IDictionary.TryGetValue(...) makes code simpler and more efficient:

private readonly IDictionary mDictionary = new Dictionary();

public void IncrementCounter(string counterKey)
{
    if(mDictionary.ContainsKey(counterKey))
    {
        int existingCount = mDictionary[counterKey];

        mDictionary[counterKey] = existingCount + 1;
    }
    else
    {
        mDictionary.Add(counterKey, 1);
    }
}

public void TryIncrementCounter(string counterKey)
{
    int existingCount;
    if (mDictionary.TryGetValue(counterKey, out existingCount))
    {
        mDictionary[counterKey] = existingCount + 1;
    }
    else
    {
        mDictionary.Add(counterKey, 1);
    }
}

And all thanks to the out parameter.