Ruby Intro Presentation

Ruby: An Introduction Jorge Chao University of New Orleans Slides available as PDF @ www.cs.uno.edu/~jchao/RubyIntro.pdf

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Matz •

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The Ruby Godfather

Some Ruby History • Ruby was developed in 1993 by Yukihiro “Matz” Matsumoto.

• His intention was to create “a scripting language more powerful than Perl, and more object-oriented than Python.”

• Bonus: Unlike Perl, you code doesn’t look

like a giant regular expression when you’ve finished.

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What is Ruby? • Ruby is an Object Oriented scripting language

• In Ruby, everything is an object • There is no notion of a primitive in Ruby, as in Java.

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irb • Interactive Ruby Shell. All of the terminal screenshots in this presentation are from irb. Its the best way to prototype and informally test your code.

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Really Object Oriented

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Really Object Oriented • No need to declare variables beforehand.

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Dynamic Typing • Sometimes called ‘Duck Typing’ or ‘Lazy Typing,’ if you’re a meanie.

• If it looks like a duck, quacks like a duck, then it’s a duck.

• The interpreter will assign types to

variables dynamically based on context.

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Dynamic Typing • This also means the interpreter can

allocate more memory for a variable.

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Built-in Types • Numbers are represented by either the

Fixnum, Bignum or Float types (all children of Numeric).

• Fixnum holds 32-bit Integer values • Fixnum overflows upconvert to Bignum, which is considered an infinite-length bitstring with 2’s compliment notation.

• Float is used for representing real numbers. Thursday, April 28, 2011

Numbers • Basic Numeric Operations

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Numbers • In Ruby, the analog to the incrementor operator in C or Java, i++, is i += 1.

• This can be done for any basic arithmetic operation.

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Numbers • Ruby makes an object of type Float any time a decimal point is used.

• The number must have a digit following the decimal, as Ruby can perform class operations on numbers.

• Ruby implicitly casts the result of an

arithmetic operation between a Float and a Fixnum to a Float.

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Strings • Ruby has great built in String manipulation facilities. Dots, dots everywhere.

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Strings • Incomplete list of built in String functions • % * + << <=> == =~ capitalize

center chomp chop concat count crypt delete downcase dump each empty? end_regexp eql? gsub hash include? index insert intern is_complex_yaml? length match oct quote replace reverse scan scanf size slice split squeeze strip sub swapcase to_f to_i to_s to_str to_sym to_yaml tr tr_s upcase upto

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Data Structures • Arrays and Hashes • Arrays can be initialized empty, or with values.

• Arrays can be combined using the +

operator or array.concat(other_array)

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Arrays • Basic array manipulation

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Hashes • Some basic hash manipulation, notice the use of :symbols, I’ll cover them in a minute.

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Iterators • What would collections of things be if we couldn’t iterate over them?

• Most iteration in Ruby is done using a do block.

• All iterations in Ruby are accomplished by passing callback closures to container methods.

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Iteration Examples • Collection.each • Similar to a foreach loop.

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More Iterators • Fixnum.times and Range.each can be used to iterate a fixed number of times, similar to a for (i = 0; i < 10; i++) construct.

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Classes • Classes start with the class keyword, end them with...end.

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Using my_class.rb • Load the newly created class into irb, and test its functionality.

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Essence Vs. Ceremony • An idea from Stu Halloway at Relevance Inc. • “Good Code is the opposite of legacy code: it captures and communicates essence while omitting ceremony (irrelevant detail).”

• The design philosophy of the language

determines what kind of code you write with it.

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Essence Vs. Ceremony • Ceremony is code unrelated to the task at hand. Ceremony is found everywhere:

• • • • •

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Factory Patterns (Java) Getters and setters (Java) Verbose exception handling (Java) Special syntax for class and instance variables (Ruby) Special syntax for ALL types of variables (Perl %$@, etc.)

Ruby != Java • Writing Ruby with Java like ceremony.

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This Time With Feeling • The same thing for less. • Making readers and writers for attributes.

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Accessors • Assessors in Ruby enforce the Uniform

Access Principle which states: “All services offered by a module should be available through a uniform notation, which does not betray its implementation.”

• :attr_accessor creates getters and setters for instance variables, preventing direct access to them. Its good to stay DRY.

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Blocks and Closures • Lets make our own iterator:

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Blocks and Closures • In the Array.iterate! example, the Array

object was extended at runtime with new functionality.

• When iterate! is called on array in this

block context, when the yield statement is reached it passes the code (and variable) in the block to the method.

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yield Example • A Lotus Notes Domino email server led to this next example:

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yield for Layouts • Rails uses yield to insert your page content inside a page layout.

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Symbols • What is a symbol? The variable name

passed to the attr_accesor and the variable used in the hash example are both symbols.

• Symbols in Ruby always start with a : • :a_symbol • Why use symbols? Thursday, April 28, 2011

Why Symbols? • :symbols are defined as a way to efficiently have descriptive names while saving the space one would use to generate a string for each naming instance.

• In Ruby, and much more in Rails, symbols

will be used to identify constructs that are used frequently (HTTP :get comes to mind)

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Oh! The Savings! • :symbols are a great way to conserve memory

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More on Symbols • Kevin Clark, Ruby Developer says: • “The intention of symbols are for

identification of (user-level, primarily) constructs: a slot in a hash, a method, an option, etc.”

• That’s the great thing about symbols, they can refer to variables or methods.

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Object Reflection • Object reflection: “The process by which a program can observe (type introspection) and modify its own structure and behavior at runtime.”

• Reflection allows inspection of classes, inheritance hierarchies, methods, etc. without prior knowledge.

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Object Reflection • Reflection also allows instantiation of new objects and invocation of methods.

• How does Ruby handle reflection? • Let’s look at how we would do it in C or Java first.

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Dispatch Table in C

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Reflection, Java Style

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Reflective Rubies • Create instance methods in a module or helper class

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Using Object.send • Object.send takes a symbol or string as parameter.

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More on Reflection • respond_to?(method) checks if a class or instance can call the method passed

• kind_of?(object) checks if the class or

instance is of that type (inheritance too!)

• instance_of?(object) checks if the caller is of that particular type.

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Examples • Some examples of querying an instance about itself

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More Object Inspection • Some other helpful inspection methods

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Inheritance Inspection • superclass and ancestors work differently

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Inheritance • Inheritance works as you would expect in an object-oriented language.

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Testing Inheritance • Same as it ever was.

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Documentation as a Ransom Note

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Ruby Documentation • Some resources for great Ruby documentation:

• http://www.ruby-doc.org/core/ • Ruby Homepage: • http://www.ruby-lang.org/en/ • Ruby tutorial as told by foxes: • http://poignantguide.net/ruby/ Thursday, April 28, 2011

Finally • An example of a Ruby tutorial on the web (why’s poignant guide to Ruby)

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Thanks for Listening

• Next time we’ll see if Rails is really worth the hype (spoiler: it is).

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