book

Head First Ruby

Name: Head First Ruby
Author: Jay McGavren
ISBN: 9781449372675

by Jay McGavren

August 2015

Beginner

572 pages

13h 48m

English

O'Reilly Media, Inc.

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Dedication
Author of Head First Ruby
How to Use This Book: Intro
Who is this book for?Who should probably back away from this book?We know what you’re thinkingWe know what your brain is thinkingMetacognition: thinking about thinkingHere’s what WE didHere’s what YOU can do to bend your brain into submissionRead meAcknowledgmentsSafari® Books Online
1. More with Less: Code the Way You Want
The Ruby philosophyGet RubyUse RubyUse Ruby—interactivelyUsing the irb shellYour first Ruby expressionsMath operations and comparisonsStringsVariablesEverything is an object!Calling a method on an objectLet’s build a gameInput, storage, and outputRunning scriptsComments“puts” and “print”Method arguments“gets”Parentheses are optional on method callsString interpolationWhat’s in that string?Inspecting objects with the “inspect” and “p” methodsEscape sequences in stringsCommonly used escape sequencesCalling “chomp” on the string objectWhat methods are available on an object?Generating a random numberConverting to stringsRuby makes working with strings easyConverting strings to numbersCommon conversionsConditionalsThe opposite of “if” is “unless”LoopsLet’s try running our game!Your Ruby ToolboxUp Next...
2. Methods and Classes: Getting Organized
Defining methodsCalling methods you’ve definedMethod namesParametersOptional parametersReturn valuesImplicit return valuesReturning from a method earlySome messy methodsToo many argumentsToo many “if” statementsDesigning a classWhat’s the difference between a class and an object?Your first classCreating new instances (objects)Breaking up our giant methods into classesThe object-oriented approachCreating instances of our new animal classesUpdating our class diagram with instance methodsOur objects don’t “know” their names or ages!Too many arguments (again)Local variables live until the method endsInstance variables live as long as the instance doesEncapsulationAttribute accessor methodsUsing accessor methodsAttribute writers and readersSymbolsAttribute writers and readers in actionEnsuring data is valid with accessorsErrors—the “emergency stop” buttonUsing “raise” in our attribute writer methodsOur complete Dog classYour Ruby ToolboxUp Next...
3. Inheritance: Relying on Your Parents
Copy, paste... Such a waste...Mike’s code for the virtual test-drive classesInheritance to the rescue!Defining a superclass (requires nothing special)Defining a subclass (is really easy)Adding methods to subclassesSubclasses keep inherited methods alongside new onesInstance variables belong to the object, not the class!Overriding methodsBringing our animal classes up to date with inheritanceDesigning the animal class hierarchyCode for the Animal class and its subclassesOverriding a method in the Animal subclassesWe need to get at the overridden method!The “super” keywordA super-powered subclassDifficulties displaying DogsThe Object classWhy everything inherits from the Object classOverriding the inherited methodYour Ruby ToolboxUp Next...
4. Initializing Instances: Off to a Great Start
Payroll at ChargemoreAn Employee classCreating new Employee instancesA division problemDivision with Ruby’s Fixnum classDivision with Ruby’s Float classFixing the salary rounding error in EmployeeFormatting numbers for printingFormat sequencesFormat sequence typesFormat sequence widthFormat sequence width with floating-point numbersUsing “format” to fix our pay stubsWhen we forget to set an object’s attributes...“nil” stands for nothing“/” is a methodThe “initialize” methodEmployee safety with “initialize”Arguments to “initialize”Using optional parameters with “initialize”“initialize” does an end-run around our validation“initialize” and validationCall other methods on the same instance with “self”When “self” is optionalImplementing hourly employees through inheritanceRestoring “initialize” methodsInheritance and “initialize”“super” and “initialize”Same class, same attribute valuesAn inefficient factory methodClass methodsOur complete source codeYour Ruby ToolboxUp Next...
5. Arrays and Blocks: Better Than Loops
ArraysAccessing arraysArrays are objects, too!Looping over the items in an arrayThe repeating loopEliminating repetition...the WRONG way...Chunks of code?BlocksBlocks are mind-bending stuff. But stick with it!Defining a method that takes blocksYour first blockFlow of control between a method and blockCalling the same method with different blocksCalling a block multiple timesBlock parametersUsing the “yield” keywordBlock formatsThe “each” methodThe “each” method, step-by-stepDRYing up our code with “each” and blocksBlocks and variable scopeUsing “each” with the “refund” methodUsing “each” with our last methodOur complete invoicing methodsWe’ve gotten rid of the repetitive loop code!Utilities and appliances, blocks and methodsYour Ruby ToolboxUp Next...
6. Block Return Values: How Should I Handle This?
A big collection of words to search throughOpening the fileSafely closing the fileSafely closing the file, with a blockDon’t forget about variable scope!Finding array elements we want, with a blockThe verbose way to find array elements, using “each”Introducing a faster method...Blocks have a return valueHow the method uses a block return valuePutting it all togetherA closer look at the block return valuesEliminating elements we don’t want, with a blockThe return values for “reject”Breaking a string into an array of wordsFinding the index of an array elementMaking one array that’s based on another, the hard wayMaking one array based on another, using “map”Some additional logic in the “map” block bodyThe finished productYour Ruby ToolboxUp Next...
7. Hashes: Labeling Data
Counting votesAn array of arrays...is not idealHashesHashes are objectsHashes return “nil” by defaultnil (and only nil) is “falsy”Returning something other than “nil” by defaultNormalizing hash keysHashes and “each”A mess of method argumentsUsing hashes as method parametersHash parameters in our Candidate classLeave off the braces!Leave out the arrows!Making the entire hash optionalTypos in hash arguments are dangerousKeyword argumentsUsing keyword arguments with our Candidate classRequired keyword argumentsYour Ruby ToolboxUp Next...

8. References: Crossed Signals
Some confusing bugsThe heapReferencesWhen references go wrongAliasingFixing the astronomer’s programQuickly identifying objects with “inspect”Problems with a hash default objectWe’re actually modifying the hash default object!A more detailed look at hash default objectsBack to the hash of planets and moonsOur wish list for hash defaultsHash default blocksHash default blocks: Assigning to the hashHash default blocks: Block return valueHash default blocks: A shortcutThe astronomer’s hash: Our final codeUsing hash default objects safelyHash default object rule #1: Don’t modify the default objectHash default object rule #2: Assign values to the hashThe rule of thumb for hash defaultsYour Ruby ToolboxUp Next...
9. Mixins: Mix It Up
The media-sharing appThe media-sharing app...using inheritanceOne of these classes is not (quite) like the othersOption one: Make Photo a subclass of ClipOption two: Copy the methods you want into the Photo classNot an option: Multiple inheritanceUsing modules as mixinsMixins, behind the scenesCreating a mixin for commentsUsing our comments mixinA closer look at the revised “comments” methodWhy you shouldn’t add “initialize” to a mixinMixins and method overridingAvoid using “initialize” methods in modulesUsing the Boolean “or” operator for assignmentThe conditional assignment operatorOur complete codeYour Ruby ToolboxUp Next...
10. Comparable and Enumerable: Ready-Made Mixes
Mixins built into RubyA preview of the Comparable mixinChoice (of) beefImplementing a greater-than method on the Steak classConstantsWe have a lot more methods to define...The Comparable mixinThe spaceship operatorImplementing the spaceship operator on SteakMixing Comparable into SteakHow the Comparable methods workOur next mixinThe Enumerable moduleA class to mix Enumerable intoMixing Enumerable into our classInside the Enumerable moduleYour Ruby ToolboxUp Next...
11. Documentation: Read the Manual
Learning how to learn moreRuby’s core classes and modulesDocumentationHTML documentationListing available classes and modulesLooking up instance methodsInstance methods denoted with # in the docsInstance method documentationArguments in call signaturesBlocks in call signaturesRead the docs for the superclass and mixins, too!Read the docs for the superclass and mixins, too! (continued)Pool PuzzlePool Puzzle SolutionLooking up class methodsClass method documentationDocs for a class that doesn’t exist?!The Ruby standard libraryLooking up classes and modules in the standard libraryWhere Ruby docs come from: rdocWhat rdoc can deduce about your classesAdding your own documentation, with commentsThe “initialize” instance method appears as the “new” class methodYour Ruby ToolboxUp Next...
12. Exceptions: Handling the Unexpected
Don’t use method return values for error messagesUsing “raise” to report errorsUsing “raise” by itself creates new problemsExceptions: When something’s gone wrongRescue clauses: A chance to fix the problemRuby’s search for a rescue clauseUsing a rescue clause with our SmallOven classWe need a description of the problem from its sourceException messagesOur code so far...Different rescue logic for different exceptionsException classesSpecifying exception class for a rescue clauseMultiple rescue clauses in one begin/end blockUpdating our oven code with custom exception classesTrying again after an error with “retry”Updating our oven code with “retry”Things you want to do no matter whatThe ensure clauseEnsuring the oven gets turned offYour Ruby ToolboxUp Next...
13. Unit Testing: Code Quality Assurance
Automated tests find your bugs before someone else doesA program we should have had automated tests forTypes of automated testsMiniTest: Ruby’s standard unit-testing libraryRunning a testTesting a classA closer look at the test codeRed, green, refactorTests for ListWithCommasGetting the test to passAnother bug to fixTest failure messagesA better way to assert that two values are equalSome other assertion methodsRemoving duplicated code from your testsThe “setup” methodThe “teardown” methodUpdating our code to use the “setup” methodYour Ruby ToolboxUp Next...
14. Web Apps: Serving HTML
Writing web apps in RubyOur task listProject directory structureBrowsers, requests, servers, and responsesSinatra takes requestsDownloading and installing libraries with RubyGemsInstalling the Sinatra gemA simple Sinatra appYour computer is talking to itselfRequest typeResource pathSinatra routesMultiple routes in the same Sinatra appA route for the list of moviesMaking a movie list in HTMLAccessing the HTML from SinatraA class to hold our movie dataSetting up a Movie object in the Sinatra appERB embedding tagsThe ERB output embedding tagEmbedding a movie title in our HTMLPool PuzzlePool Puzzle SolutionThe regular embedding tagLooping over several movie titles in our HTMLLetting users add data with HTML formsGetting an HTML form for adding a movieHTML tablesCleaning up our form with an HTML tableThere’s still more to doYour Ruby ToolboxUp Next...
15. Saving and Loading Data: Keep It Around
Saving and retrieving form dataOur browser can GET the form...... But it needs to POST the responseSetting the HTML form to send a POST requestSetting up a Sinatra route for a POST requestConverting objects to and from strings with YAMLSaving objects to a file with YAML::StoreSaving movies to a file with YAML::StoreA system for finding Movies in the YAML::StoreNumeric IDs for MoviesFinding the next available movie IDA class to manage our YAML::StoreUsing our MovieStore class in the Sinatra appTesting the MovieStoreLoading all movies from the MovieStoreLoading all movies from the MovieStore (continued)Loading all movies in the Sinatra appBuilding HTML links to individual moviesBuilding HTML links to individual movies (continued)Named parameters in Sinatra routesUsing a named parameter to get a movie’s IDDefining routes in order of priorityFinding a Movie in the YAML::StoreAn ERB template for an individual movieFinishing the Sinatra route for individual moviesLet’s try it all out!Our complete app codeYour Ruby ToolboxUp Next...
A. Leftovers: The top ten topics (we didn’t cover)
#1 Other cool librariesRuby on RailsdRubyCSV#2 Inline if and unless#3 Private methods#4 Command-line arguments#5 Regular expressions#6 Singleton methods#7 Call any method, even undefined ones#7 Call any method, even undefined ones (continued)#8 Automating tasks with Rake#9 Bundler#10 Other books
B. This isn’t goodbye
C. O’reilly®: Ruby
What will you learn from this book?What’s so special about this book?
Index
About the Author
Copyright

Content preview from Head First Ruby

Chapter 8. References: Crossed Signals

Ever sent an email to the wrong contact? You probably had a hard time sorting out the confusion that ensued. Well, Ruby objects are just like those contacts in your address book, and calling methods on them is like sending messages to them. If your address book gets mixed up, it’s possible to send messages to the wrong object. This chapter will help you recognize the signs that this is happening, and help you get your programs running smoothly again.

Some confusing bugs

The word continues to spread—if someone has a Ruby problem, your company can solve it. And so people are showing up at your door with some unusual dilemmas...

This astronomer thinks he has a clever way to save some coding. Instead of typing my_star = CelestialBody.new and my_star.type = 'star' for every star he wants to create, he wants to just copy the original star and set a new name for it.

But the plan seems to be backfiring. All three of his CelestialBody instances are reporting that they have the same name!

The heap

The bug in the star catalog program stems from an underlying problem: the developer thinks he’s working with multiple objects, when actually he’s operating on the same ...

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