Combine static and dynamic types — visual studio magazine euro pound exchange rate forecast


In the case of late binding, the application would continue to work as long as a new version of a component had all the same methods that previous versions had, even if it contained new, non-private methods usd vnd. You accomplished this by declaring a variable as Object. You also had to create the variable using the CreateObject function with ProgId as a parameter. This meant that the Visual Basic runtime would check for existence of a method or a property only at run time, during the execution. The code would execute without any problems as long as the object supported the function or property in question.

The style of programming where the type of the method is determined by the inspection of the signature of its methods and properties, rather then by explicit static relationships between objects, is known as duck typing.

The name derives from the cliché: "If it walks like a duck and quacks like a duck, it must be a duck."

Everything works fine, as long as the object has the member that corresponds to what client code expects. Several modern languages, such as Ruby and Python, as well as older languages like Smalltalk, permit this style of programming. Devotees of dynamically-typed languages emphasize the flexibility and productivity you can obtain from this approach, and praise it over the benefits that static-type checking can bring. People who promote late binding usually cite unit testing as the best guard against introducing programming errors usd to aud forecast. In dynamically-typed languages, function calls are resolved at run time, which permits treating objects in polymorphic manner, but without any interface or implementation inheritance relationship between the objects.

The .NET versions of VB permit a similar style of programming; however, they also let you disable late-bound programming by using the Option Strict On statement. Microsoft introduced this option with the first version of VB.NET. In pre-.NET versions of VB, anything you declare as Object is late bound free quotes for car insurance. Placing Option Strict On at the top of a file effectively turns off late binding in that file.

You need to set Option Strict to Off for this code to compile. This code executes fine as long as the officeObject parameter was created as an Excel.Worksheet or Word.Document, due to the fact that both of these objects have both CheckSpelling and SaveAs methods (see Figure 1).

It’s also possible to write this code with Option Strict on. However, doing so would make it far more verbose code-wise, to accomplish the same behaviour python example programs. Consider this code, which is based on reflection:

Reflection enables you accomplish everything you could do in pre-.NET versions of VB with late binding—and more. However, it does require that you write substantially more code to do so. In this case, the entire sample has only two lines, but the difference in quantity of code is significant. Now imagine you have to write a lot of code similar to this. The less verbose variant would be far preferable usd to inr live chart. If you didn’t use reflection, the only solution in strict mode would be to overload a pair of methods:

In a more common situation, you could resolve this by making both Document and Worksheet inherit the same base class or implement the same interface. Extract Interface is a standard refactoring technique. In this case, you don’t have source for Office Automation Libraries, so the Extract Interface approach won’t work here. You also cannot modify the Document or Worksheet class, so you need to find a different solution.

Visual Basic behaves like a statically-typed language once you activate Option Strict, much as C# or Java do what is a binary system. A unique feature of VB when compared to other static or dynamic languages is that VB lets you specify this option at the file level. This means that you can mix files written in static and dynamic style in the same project.

This gives you a great deal of flexibility when you write code. You can sum up Microsoft’s approach to typing with this sentence: "Static typing where possible, dynamic typing when needed." This leads us to an interesting way of considering the problem of how to approach the static versus dynamic typing issue: If you can isolate the dynamic elements from the static ones into separate files, you can keep code strict in all but the parts of your application that absolutely require it.

Before I go into more detail about how to do this, it might be helpful to review some aspects of VB as dynamic language. Some dynamic languages go further than Visual Basic with the dynamic paradigm gbp usd rate today. For example, they will also let you modify types by adding properties and methods "on the fly" at run time. You cannot implement similar functionality in VB without using the services provided by the Reflection.Emit namespace. This means you can be fairly certain that all the types you will encounter exist at the moment of compiling your program. Even in cases where you load some types dynamically, these types were probably compiled and created as static types, and there already exists a physical assembly or DLL containing these types. It is highly probable that these types were created intentionally to represent a certain defined entity, along usual OO design and analysis guidelines.

These facts lead you to an interesting conclusion: In Visual Basic, you interact with static types underneath, even when writing dynamic code gbp to usd exchange rate forecast. Now let’s return to the CheckSpellingAndSave code snippet. This code interacts with two types: Word.Document and Excel.Worksheet, both from the Office automation library currency conversion usd to aud. Knowing this, it makes sense to provide a statically-typed wrapper over the dynamic code. This means the code that interacts with the wrapper never knows what happens underneath, nor does it need to. Client code treats your wrapper like any other static type, remaining oblivious to the fact that you used the wrapper to encapsulate dynamic code.

The sample handles two types: Document and Worksheet. The types exhibit some common behavior—they both implement CheckSpelling and SaveAs methods—but they don’t share any common types, except the ultimate base type, Object, which is common to every other type in .NET. You cannot access the services these objects provide in a common way.

You could simply declare an interface if you had the source code for these two classes. For example, you could name it IOfficeWrapper, and then declare all common methods for Document and Worksheet in that interface. You would also make Document and Worksheet implement the IOfficeWrapper interface. This is typical Extract Interface refactoring. This approach enables you to see Document and Worksheet through a common interface and treat them in a uniform manner. This code creates an IOfficeWrapper interface, enabling it to contain all the methods used in a common manner:

You can’t change either the Excel.Worksheet or the Word.Document classes, so you need to create a new class that implements this interface. You need to make this new class delegate calls to the original officeObject. You also need to write this class in a dynamically-typed style so it can treat both the Worksheet and Document objects in the same way 1 usd in euro. Finally, place the class in a separate file and deactivate Option Strict.

p>You provide a wrapper with a constructor, so it can receive an officeObject and keep a reference to the officeObject in a private field. CheckSpelling and SaveAs method delegate calls only to a reference of original officeObject maintained as a field in our OfficeWrapper class (see Listing 2).