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n previous chapters we ve looked at and worked with Ruby from a low-level perspective by working directly with classes, objects, and functions. Each line of code we ve used in the small projects so far has been written specifically for that project from scratch. In this chapter, we ll look at how to build larger projects with Ruby, and how to reuse code written previously. Finally, we ll look at how to use code already written and prepared by other developers within your own applications, so that you don t need to reinvent the wheel every time you create a new program. This chapter is about the bigger picture: dealing with projects and libraries.

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As you become more familiar with Ruby and find more uses for it, it s likely that you ll want to move from writing single small programs (with fewer than 100 or so lines) to more complex applications and systems made up of multiple parts. Larger applications and systems therefore often become known as projects, and are managed in a different way than simple one-file scripts. The most common way to separate functionality in Ruby is to put different classes in different files. This gives you the ability to write classes that could be used in multiple projects simply by copying the file into your other project.

In a lm, the opening title sequence establishes the mood and tone of the story to come. You can achieve a similar effect by adding graphics to the Title slide. Apply the same style to the Title slide that you did to the other slides in Act I. For example, if you use the photographic design technique for the Act I slides, use the same style for the Title slide. Then apply the same technique you use for the Title slide to a Closing Credits slide that will remain on screen when you nish your presentation. To create a closing slide now, on the Home tab, click New Slide, and on the drop-down menu, click Blank. Now add a simple image or a line of text that you want the audience to remember after the presentation. This slide might include your organization s name, your contact information, a Web address, or a simple image that conveys the theme of the presentation.

Consider this code:

Usually, a loop simply executes a block until its condition becomes false, or until it has used up all sequence elements but sometimes you may want to interrupt the loop, to start a new iteration (one round of executing the block), or to simply end the loop.

puts "This is a test".vowels.join('-')

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If you try to execute this code, you ll get an error complaining that the vowels method is not available for the "This is a test" object of class String. This is true because Ruby doesn t provide that method. Let s write an extension to the String class to provide it:

If this definition were included in the same file as the prior puts code, the result would be as follows:

To end (break out of) a loop, you use break. Let s say you wanted to find the largest square (an integer that is the square of another integer) below 100. Then you start at 100 and iterate downwards to 0. When you ve found a square, there s no need to continue, so you simply break out of the loop: from math import sqrt for n in range(99, 0, -1): root = sqrt(n) if root == int(root): print n break If you run this program, it will print out 81, and stop. Notice that I ve added a third argument to range that s the step, the difference between every pair of adjacent numbers in the sequence. It can be used to iterate downwards as I did here, with a negative step value, and it can be used to skip numbers: >>> range(0, 10, 2) [0, 2, 4, 6, 8]