.NET/Java PDF, Tiff, Barcode SDK Library

txt") By default, fields in a class are immutable, which means once they have been bound to a value, the value can be rebound to another value For F# records with mutable fields and NET objects, this does not mean their internal state cannot change; it simply means you cannot replace the whole value to which the field is bound You can see this in the previous example; if the file you are creating doesn t exist, the file will be created, changing the value of the Exists flag to true However, you cannot set the field innerFile to be another instance of the FileInfo object From time to time, it can be useful to rebind a field to another value To allow this to happen, F# provides the keyword mutable; when a field is defined as mutable, it can be rebound whenever the programmer chooses.

barcode data entry excel, creare barcode con excel 2013, free barcode generator excel, how to create barcodes in excel 2013 free, how to make barcodes in excel 2016, create barcode excel 2013, free excel 2007 barcode add in, how to add barcode font to excel 2007, barcode font for excel, barcode in excel 2007,

Figure 1-25. RCX Rotation Sensor You can see the vanes and the electronics on the PCB in Figure 1-26.

Summary

The following example illustrates its usage In this example, you see that the mutable keyword is applied to the FileInfo field so that you can change.

Figure 1-26. Rotation Sensor breakdown The RCX Rotation Sensor has one big advantage over the NXT. Because it hasn t been combined with an elaborate gear train and electric motor, the RCX Rotation Sensor rotates almost without friction. If you want to measure the rotation of something like a hamster wheel, you need the RCX Rotation Sensor.

the instance of the object it refers to later. You see that if the file does not exist, it is replaced by the first file available in the directory. #light open System.IO type File4 = class val path: string val mutable innerFile: FileInfo new(path) as x = { path = path ; innerFile = new FileInfo(path) } then if not x.innerFile.Exists then let dir = x.innerFile.Directory in let files = dir.GetFiles() in if files.Length > 0 then x.innerFile <- files.(0) else failwith "no files exist in that dir" end let myFile4 = new File4("whatever2.txt")

While Ajaxesque techniques have been used for many years, the recent adoption of the XMLHttpRequest object by modern browsers has ushered in a new era of developing rich Web applications. In this chapter, we established the basics of working with the heart of Ajax, the XMLHttpRequest object. At this point, you know the methods and properties of the XMLHttpRequest object, and we ve shown you some simple examples of their use. As you can see, the object is pretty straightforward and hides much of its complexity from you. Combined with a healthy dose of JavaScript and some basic DOM manipulation, Ajax allows for a level of interactivity previously unmatched on the Web. As mentioned in 1, with XMLHttpRequest you are no longer limited to complete page refreshes and synchronous conversations with your server. In the upcoming chapters, we ll show you how to combine your existing expertise of server-side technologies with the unique capabilities of XMLHttpRequest to provide highly interactive Web applications.

So far you ve defined classes using the explicit syntax for constructors. A recent enhancement to F# is called implicit class construction or the compact class syntax. This allows a class to implicitly define a construction sequence through a series of let bindings prior to the member definitions of the class. These bindings are private to the class. For example, you can define the File1 example from the previous section simply by using the following: type File1(path) = class let innerFile = new FileInfo(path) member x.InnerFile = innerFile end let myFile1 = new File1("whatever.txt") Classes using implicit class construction have a tuple of arguments such as path after the name of the type constructor. Furthermore, the body of the class may contain let bindings, which are always private to the class. Here you have also added the property member InnerFile to reveal the value of the value of the innerFile. I discuss property members later in this chapter. Here is a second example: type Counter(start, increment, length) = class let finish = start + length let mutable current = start

The RCX Temperature Sensor looks like a brick with a short metal tube sticking out of it (see Figure 1-27). The temperature transducer is located inside this metal tube. We ll discuss the sensor in great detail in 5 when you make your own Temperature Sensor.