Ruby An Introduction Created by Yukihiro Matsumoto in

Ruby: An Introduction • Created by Yukihiro Matsumoto in 1993 (named after his birthstone) • Pure OO language (even the number 1 is an instance of a class) • Highly portable, works on Linux, UNIX, DOS, Windows 95/98/NT/2 K, Mac, etc.

Ruby: the Language • Has garbage collection. • Exception handling, like Java. • Any class or instance can be extended anytime (even during runtime) • Allows operator overloading.

Ruby: the Language • Can be extended with Ruby or low-level C. • No type declaration. • Has iterators, methods which accept blocks for user-defined control structures (like loops) • Emacs, Text. Pad, and Vim all have support available for Ruby.

Ruby - To know ruby version, on command prompt: ruby -v - You can place a ruby program directly on the command line using the -e option: % ruby -e 'puts "hello world"' hello world - More conventionally, a ruby program can be stored in a file. % echo "puts 'hello world'" > hello. rb % ruby hello. rb hello world

What is Irb? - Interactive Ruby (IRb) provides a shell for experimentation. Within the IRb shell, you can immediately view expression results, line by line. - This tool comes along with Ruby installation so you have nothing to do extra to have Irb working. - Just type irb at your command prompt and an Interactive Ruby Session will start.

Reserved Keywords

Ruby Vs Java / C++ • Ruby • C++ / Java – “Ruby”. length – strlen(“Ruby”); – s. length(); – -5. 0. abs – abs(-5. 0); – number = Math. abs(number);

Data Types

Ruby Arrays Literals of Ruby Array are created by placing a commaseparated series of object references between square brackets. A trailing comma is ignored. ary = [ “abc", 10, 3. 14, "This is a string", "last element", ] ary. each do |i| puts i end Result: abc 10 3. 14 This is a string last element

Ruby Hashes A literal Ruby Hash is created by placing a list of key/value pairs between braces, with either a comma or the sequence => between the key and the value. A trailing comma is ignored.

Ruby Ranges A Range represents an interval. A set of values with a start and an end. Ranges may be constructed using the s. . e and s. . . e literals, or with Range. new. Ranges constructed using. . run from the start to the end inclusively. Those created using. . . exclude the end value. When used as an iterator, ranges return each value in the sequence. A range (1. . 5) means it includes 1, 2, 3, 4, 5 values and a range (1. . . 5) means it includes 2, 3, 4 values.

Features Free format - You can start writing your program from any line and column. Case sensitive - Lowercase letters and uppercase letters are distinct. The keyword end, for example, is completely different from the keyword END. Comments - Anything following an unquoted #, to the end of the line on which it appears, is ignored by the interpreter. Also, to facilitate large comment blocks, the ruby interpreter also ignores anything between a line starting with =begin and another line starting with =end. This only works if the = signs are the first characters of each line. Statement delimiters - Multiple statements on one line must be separated by semicolons, but they are not required at the end of a line; a linefeed is treated like a semicolon. If a line ends with a backslash (), the linefeed following it is ignored; this allows you to have a single logical line that spans several lines. Keywords- Also known as reserved words (around 41 of them) in Ruby typically cannot be used for other purposes. You may be used to thinking that a false value may be represented as a zero, a null string, a null character, or various other things. But in Ruby, all of these *values* are true; in fact, everything is true except the reserved words false and nil. Keywords would be called "reserved words" in most languages and they would never be allowed as identifiers. The Ruby parser is flexible and does not complain if you prefix these keywords with @, @@ or $ prefixes and use them as instance, class or global variable names. The best practice is to treat these keywords as reserved.

Strings # p 003 rubystrings. rb =begin Ruby Strings In Ruby, strings are mutable =end # Can use " or ' for Strings, but ' is more efficient puts 'Hello World' # String concatenation puts 'I like' + ' Ruby' # Escape sequence puts 'It's my Ruby' # New here, displays the string three times puts 'Hello' * 3 # Defining a constant PI = 3. 1416 puts PI #command using backticks puts `dir`

- If puts is passed an object that is not a string, puts calls the to_s method of that object and prints the string returned by that method. - In Ruby, strings are mutable. They can expand as needed, without using much time and memory. Ruby stores a string as a sequence of characters.

Variables and Constants Variables in Ruby can contain data of any type. You can use variables in your Ruby programs without any declarations. Variable name itself denotes its scope (local, global, instance, etc. ). A local variable (declared within an object) name consists of a lowercase letter (or an underscore) followed by name characters (sunil, _z, hit_and_run). An instance variable (declared within an object always "belongs to" whatever object self refers to) name starts with an ''at'' sign (''@'') followed by a name (@sign, @_, @Counter). A class variable (declared within a class) name starts with two ''at'' signs (''@@'') followed by a name (@@sign, @@_, @@Counter). A class variable is shared among all objects of a class. Only one copy of a particular class variable exists for a given class. Class variables used at the top level are defined in Object and behave like global variables. Class variables are rarely used in Ruby programs. Global variables start with a dollar sign (''$'') followed by name characters. A global variable name can be formed using ''$-'' followed by any single character ($counter, $COUNTER, $-x). Ruby defines a number of global variables that include other punctuation characters, such as $_ and $-K. Constants A constant name starts with an uppercase letter followed by name characters. Class names and module names are constants, and follow the constant naming conventions. Examples: PI=3. 1416

Ruby Types

Ruby Pseudo Variables

Ruby Predefined Variables

Ruby: A Demonstration #Person Class class Person attr_accessor : name, : age def initialize(name, age) @name = name @age = age. to_i end def inspect "#@name (#@age)" end #Usage of the class p 1 = Person. new('elmo', 4) p 2 = Person. new('zoe', 7)

Advantages using Ruby against Java and C++ • Support Regular Expression • Cleaner code – No need to declare variables – Simple syntax (semi-colon is optional) – Every thing is an object, even a number. No need to call separate function. – Simple object get/set methods declaration

Advantages (continue) Better Access Control – Dynamic access control – Private methods never accessible directly by another object • Portable and extensible with third-party library • Interactive environment