Professional .NET 2.0 Generics

7.3. Boxing and Constraints

In some cases, the application of type constraints will actually prevent your value type parameters from being boxed. Suppose, for example, you had the following interface and structure that you wanted to use to manage stock prices:

[VB code]
Public Interface IPriceTicker
    Sub UpdatePrice(ByVal newPrice As Double)
    Function ToString() As String
End Interface

Public Structure Stock
    Implements IPriceTicker
    Private currentPrice As Double

    Public Sub UpdatePrice(ByVal newPrice As Double) _
                                 Implements IPriceTicker.UpdatePrice
        Console.Out.WriteLine("Updating With Price: {0}", newPrice)
        currentPrice = newPrice
    End Sub

    Public Overrides Function ToString() As String Implements IPriceTicker.ToString
        Return currentPrice.ToString()
    End Function

End Structure

[C# code]
public interface IPriceTicker {
    void UpdatePrice(double newPrice);
}

public struct Stock : IPriceTicker {
    Private double currentPrice;

    public void UpdatePrice(double newPrice) {
        Console.Out.WriteLine("Updating With Price: {0}", newPrice);
        currentPrice = newPrice;
    }

    public override string ToString() {
        return currentPrice.ToString();
    }
}

The Stock structure introduced here is meant to represent a simple value type that, through its implementation of the IPriceTicker interface, allows clients to change the value of a stock. Now, put together a couple of clients that will create a Stock and feed it some new prices:

[VB code] Public Class PriceTest Public Sub ProcessPrices1(Of T As New)(ByVal prices As Double()) ...