and other languages…

 Array literals/initialization a = [1,2,3] a2 = [-10..0, 0..10] a3 = [[1,2],[3,4]] a4 = [w*h, w, h] a5 = [] empty = Array.new zeros = Array.new(5, 0)  Arrays are heterogeneous  length and size return # of elements  Access beyond end of array returns nil  Elements can be accessed similar to strings  Arrays can be dynamically resized (can assign past the end of the array)  Use | and & for union and intersection Compare to Java/C++

 words = %w[here we go again] => [‘here’,’we’,’go’,’again’]  Use << to append  Useful functionality alphabet = ('A'..'Z').to_a alphabet.each {|c| print c }  Not covered: lots of methods, like clear, empty?, compact!, sort, sort!, pop, push, reverse, etc.

 Immutable, interned string (only one copy)  Colon-prefixed, e.g., :one  Commonly used as hash key  Also stores names of classes, methods and variables in symbol table – more efficient than storing as string, can be used with reflection  If your code is using a string as a unique identifier, consider using a symbol instead  Methods available to convert between string and symbol Get used to symbols, they’re used a lot

 Aka maps, associative arrays colors = { :Cyndi => "orange", :Karyl => "purple" } colors2 = { "Cyndi" => "orange", "Karyl" => "purple" } colors3 = { Cyndi: "orange", Karyl: "purple" } puts colors3[:Cyndi] colors.each do |key, value| puts "#{key}'s favorite color is #{value}" end  Best to use immutable objects as keys  Not covered: hash codes Hashes supported directly in Perl, Python (dictionary) and Ruby and in class libraries of Java, C++ and C# Required sometimes, e.g., Python

 Which is better if need to access items in order?  Which is useful for direct access?  Hash: useful for “paired” data

 Purpose determine if a value is in or out of range iteration  Can be any value that implements function (like CompareTo… why is this needed?)  includes 10  1…10 excludes 10 coldwar = coldwar.include? birthdate.year (1..3).to_a parentheses required, else just applies to 3 Subrange introduced in Pascal, also used in Modula-2 and Ada. Others?

 TrueClass singleton, write as true  FalseClass singleton, write as false  nil means no value. Test directly (o == nil) or with nil?  true != 1, false != 0 Compare to Java/C++/C

 FixNum. Int operations that fit in a machine word.  BigNum. Used for larger ints (FixNum will be converted automatically)  Float. Floating point values  Complex. real + imaginary  Rational. e.g., 2/3

 Language Concepts Array  Heterogeneous?  Array operations  Fixed or dynamic size Hash  key restrictions Range  operations Boolean  0/1?  Ruby Arrays  new  each Symbols Hashes Range Boolean