.NET/Java PDF, Tiff, Barcode SDK Library

The previous methods are fine for simple situations where you just want to get basic results from a remote program and don t need to interact directly with it in any way while it s running. However, sometimes you might want to pass data back and forth between two separate programs. Ruby s IO module has a popen method that allows you to run another program and have an I/O stream between it and the current program. The I/O stream between programs works like the other types of I/O streams we looked at in 9, but instead of reading and writing to a file, you re reading and writing to another program. Obviously, this technique only works successfully with programs that accept direct input and produce direct output at a command-prompt level (so not GUI applications).

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Where local variables are specific to the local scope, and global variables have global scope, object variables are so named because they have scope within, and are associated to, the current object. A demonstration of this concept was shown at the start of this section with the Square class:

As described in 7, the sketches of your Explanation slides might guide you toward adding a photograph, logo, diagram, chart, or other illustration on the individual slides. Figure 8-27 shows a Key Point slide with graphics that you ve already added (upper left), and the sketches of its three related Explanation slides. Locate and add graphics that correspond to these sketches on each of these slides, as shown in Figure 8-28. Notice that the clipboard graphics are telling a story, slide by slide, as they explain the initial Key Point slide in turn, each Explanation slide will visually introduce and summarize its subsequent Detail slides. You would apply a similar technique of building a visual story step by step if your story template and sketches call for the use of a diagram or chart on the Explanation slides.

class Square def initialize(side_length) @side_length = side_length end def area @side_length * @side_length end end

Object variables are prefixed with an @ symbol. In the Square class, you assign the side_length provided to the class to @side_length. @side_length, as an object variable, is then accessible from any other method inside that object. That s how the area method can then use @side_length to calculate the area of the square represented by the object:

FIGURE 8-27 Key Point slide with graphics already added, along with original sketches of the related

Chained assignments are used as a shortcut when you want to bind several variables to the same value. This may seem a bit like the simultaneous assignments in the previous section, except that here you are only dealing with one value: x = y = somefunction() which is the same as y = somefunction() x = y Note that the preceding statements may not be the same as x = somefunction() y = somefunction() For more information, see the section about the identity operator (is), later in this chapter.

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The results are different, even though the code to work out the area in both cases is @side_length * @side_length. This is because @side_length is an object variable associated only with the current object or instance.

When your Explanation slides feature the same underlying graphic in this example, the blank clipboard use custom layouts to make adding graphics easier, as described in Tip 3: Use Custom Layouts to Add the Same Graphic to Related Slides later in this chapter.

If you didn t fully understand the Shape/Square/Triangle example at the start of this chapter, now Tip

Instead of writing x = x + 1, you can just put the expression operator (in this case +) before the assignment operator (=) and write x += 1. This is called an augmented assignment, and it works with all the standard operators, such as *, /, %, and so on:

would be a good time to look back at it, as it used several object variables to develop its functionality.

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