How to initialize KeyValuePair object the proper way?

Question

You are not wrong you have to initialise a keyValuePair using

KeyValuePair<int, int> keyValuePair = new KeyValuePair<int, int>(1, 2);

The reason that you cannot use the object initialisation syntax ie { Key = 1, Value = 2 } is because the Key and Value properties have no setters only getters (they are readonly). So you cannot even do:

keyValuePair.Value = 1; // not allowed

Dictionaries have compact initializers:

var imgFormats = new Dictionary<string, ChartImageFormat>()
{
    {".bmp", ChartImageFormat.Bmp}, 
    {".gif", ChartImageFormat.Gif}, 
    {".jpg", ChartImageFormat.Jpeg}, 
    {".jpeg", ChartImageFormat.Jpeg}, 
    {".png", ChartImageFormat.Png}, 
    {".tiff", ChartImageFormat.Tiff}, 
};

In this case the dictionary i used to associate file extensions with image format constants of chart objects.

A single keyvaluepair can be returned from the dictionary like this:

var pair = imgFormats.First(p => p.Key == ".jpg");

KeyValuePair<int, int> is a struct, and, fortunately, it is immutable struct. In particular, this means that its properties are read only. So, you can't use object intializer for them.

Ok you have the answers. As an alternative, I prefer factory pattern similar to Tuple class, for type inference magic :)

public static class KeyValuePair
{
    public static KeyValuePair<K, V> Create<K, V>(K key, V value)
    {
        return new KeyValuePair<K, V>(key, value);
    }
}

So short becomes shorter:

var keyValuePair = KeyValuePair.Create(1, 2);