asp net 3.5unleashed

When the source type and the target type are a compiler’s primitive types, the compiler knows how to emit the necessary code to convert the object.

However, if neither type is one of the compiler’s primitive types, the compiler won’t know how to perform the conversion. For example, imagine that the FCL included a Rational data type. It might be convenient to convert an Int32 object or a Single object to a Rational object. Moreover, it also might be nice to convert a Rational object to an Int32 or a Single object.

To make these conversions, the Rational type should define public constructors that take a single parameter: an instance of the type that you’re converting from. You should also define public instance ToXxx methods that take no parameters (just like the very popular ToString method). Each method will convert an instance of the defining type to the Xxx type. Here’s how to correctly define conversion constructors and methods for a Rational type: class Rational { // Constructs a Rational from an Int32 public Rational(Int32 numerator) { ... }

// Constructs a Rational from a Single public Rational(Single value) { ... }

// Converts a Rational to an Int32 public Int32 ToInt32() { ... }

// Converts a Rational to a Single public Single ToSingle() { ... } } By invoking these constructors and methods, a developer using any programming language can convert an Int32 or a Single object to a Rational object and convert a Rational object to an Int32 or a Single object. The ability to do these conversions can be quite handy, and when designing a type, you should seriously consider what conversion constructors and methods make sense for your type.

In the previous section, I discussed how some programming languages offer operator overloading. Well, some programming languages (like C#) also offer conversion operator overloading. Conversion operators are methods that convert an object from one type to another type. You define a conversion operator method using special syntax. The following code adds four conversion operator methods to the Rational type: class Rational { // Constructs a Rational from an Int32 public Rational(Int32 numerator) { ... }

// Constructs a Rational from a Single public Rational(Single value) { ... }