A delegate is a type-safe reference to a method. Prior to C# 2.0 a delegate instance could only reference an existing named method. Now, a delegate may also point to a block of code defined in-line where the delegate is created.

Code

Now

delegate Image ImageProcessor(Image image);

Image HighContrast(Image image)
{
    Image newImage = (Image) image.Clone();
    imageLibrary.AdjustContrast(newImage);
    return newImage;
}

void Save(IEnumerable<Image> images)
{
    ImageProcessor processImage = highContrastMode
        ? (ImageProcessor)HighContrast
        : delegate (Image image) { return image; };

    int idx = 1;
    foreach(Image image in images)
        processImage(image).Save("Image" + idx++, ImageFormat.Jpeg);
}

Before

delegate Image ImageProcessor(Image image);

Image HighContrast(Image image)
{
    Image newImage = (Image) image.Clone();
    imageLibrary.AdjustContrast(newImage);
    return newImage;
}

Image NoProcessing(Image image)
{
    return image;
}

void Save(IEnumerable images)
{
    ImageProcessor processImage = highContrastMode
        ? new ImageProcessor(HighContrast)
        : new ImageProcessor(NoProcessing);

    int idx = 1;
    foreach(Image image in images)
        processImage(image).Save("Image" + idx++, ImageFormat.Jpeg);
}

Notes

• Anonymous methods can capture local variables and parameters from the enclosing method (closures), something a separate named method could only do via fields or a hand-written helper class
• The parameter list can be omitted entirely (delegate { ... }) when the body does not use the parameters
• The current compiler puts non-capturing anonymous methods into a cached singleton class named <>c; capturing ones go into a <>c__DisplayClass that holds the captured variables
• C# 2.0 also added implicit method group conversions, so ImageProcessor p = NoProcessing; no longer needs new ImageProcessor(...)

WARNING

This syntax was superseded by Lambda expressions ^{C# 3.0}.

More information

• C# Language Reference
• Anonymous Functions with C# - Debabrata Dash