However, while you index arrays with integers, you can index a hash with objects of any type: strings, regular expressions, and so on. You'll want to break this code out into separate files so the contents can be shared among different Ruby programs. What if you want to write binary data and don't want Ruby messing with it? Otherwise, the substitutions will be performed every time the literal generates a Regexp object. Similarly, the chapters on contract-driven development are worthy and echoes current practice. Andy owns his own consulting business in Raleigh, North Carolina. Parentheses are used to group regular expressions. Every library call succeeds, users never enter incorrect data, and resources are plentiful and cheap.
If you're using literals to create the Regexp object, then the options comprise one or more characters placed immediately after the terminator. The problem with this approach is that managing all these error codes can be a pain. The second and subsequent times the block is called, sum is set to the value returned by the block on the previous call. Our job is to solve problems, not spoonfeed compilers, so we like dynamic languages that adapt to us, without arbitrary, rigid rules. This list gives us a clue to the implementation. Using it, you could implement File::open again, ignoring error handling using something like the following. Because you cannot specify an object when using them, private methods can be called only in the defining class and by direct descendents within that same object.
The optional parameters follow the method name. Ruby Versions This book documents Version 1. The obvious way of adding functionality to these buttons is to create subclasses of Button and have each subclass implement its own buttonPressed method. True if the receiver and argument have the same object id. In the following code fragment, we'll start off by creating a plain old TkListbox.
That's what this book is all about. If a function calls open, then read, and finally close, and each can return an error indication, how can the function distinguish these error codes in the value it returns to its caller? There are two macros to do this wrapping, and one to retrieve your structure back out again. An approach to this problem is to define a new class, KaraokeSong, which is just like Song, but with a lyric track. If we'd allocated these strings dynamically, we'd have to write a free method to dispose of them. These patterns are called greedy, because by default they will match as much of the string as they can. Ken Coar Author, open software evangelist, and Apache developer Agile Web Development with Rails successfully straddles a fine line between being a fun-to-read introduction to Rails and Ruby and a straightforward guide to some advanced features of the platform, nicely supplanting the everchanging online documentation.
Mixins Modules have another, wonderful use. When the block exits, the file is automatically closed. One of the great things about Ruby is how well it integrates with its environment. . We can take advantage of this feature to run Ruby code from inside an editor. Modules give you two major benefits: 1.
When you release button 1, the line will be drawn in that position. The Rails core team is continuing to work on Rails. If multiple classes include that module, they'll all point to the same thing. If a method is private, it may be called only within the context of the calling object—it is never possible to access another object's private methods directly, even if the object is of the same class as the caller. For example, if you're using a hash to count the number of times each key occurs, it's convenient to have the default value be zero. What we really want is a session: a persistent state for some Web surfer. Well, possibly, but there are problems.
With arrays, the key is an integer, whereas hashes support any object as a key. What exactly is a scripting language? This should be a desktop reference for everyone who works with code for a living. So far in this book, we've been defining and using methods without much thought. Ruby uses a convention to help it distinguish the usage of a name: the first characters of a name indicate how the name is used. This is the way the C language works. You can do the same stuff in Ruby that you can in Perl or Python, and you can do it more cleanly.
But what if you want to force a pattern to match only at the start or end of a string? As we've said before, if is an expression, not a statement—it returns a value. It's time for some examples. If you define your own exceptions, you can add additional information. Comments, suggestions, errors in the text, and problems in the examples are all welcome. When we display them on our jukebox's screen, they'd look better in mixed case. If you're a new programmer, these challenges will help you learn what you need to break into the field, and if you're a seasoned pro, you can use these exercises to learn that hot new language for your next gig. To run the examples provided in this book, it is important that you install the correct version of Rails, as described in Chapter 1, Installing Rails, on page 24 To determine the version of Rails that you are running, you can issue rails -v at a command prompt.