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Basic syntax
No variable declara<ons sum = 0!
Newline is statement separator i = 1!
while i <= 10 do!
sum += i*i!
i = i + 1!
do … end instead of { … } end!
print "Sum of squares is #{sum}\n"!
Parenthesis are op<onal in method calls RUBY LUCIANO GARCÍA-­‐BAÑUELOS String interpola-on Ruby string syntax
•  Single quotes (only \' and \\)
!'Bill\'s "personal" book'"
•  Double quotes (many escape sequences)
!"Found #{count} errors\nAborting job\n""
•  %q () – similar to simple quotes
!%q<Nesting works: <b>Hello</b>>"
•  %Q () – similar to double quotes
!%Q|She said "#{greeting}"\n|"
•  “Here documents”
!<<END"
!First line"
!Second line"
!END"
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Variable names and scopes
foo
Local variable $foo
Global variable @foo
Instance variable in object @@foo
Class variable MAX_USERS
“Constant” (by conven<on) RUBY LUCIANO GARCÍA-­‐BAÑUELOS Ruby statements
if x < 10 then!
...!
elsif x < 20!
...!
else!
...!
end!
while x < 10 do!
...!
end!
Literal arrays array = [22, 34, 46, 92]!
for value in array do!
...!
end!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Ruby classes
class Point!
def initialize(x, y)!
@x = x!
@y = y!
end!
!
def x!
@x!
end!
!
def x=(value)!
@x = value!
end!
end!
p = Point.new(3,4)!
puts "p.x is #{p.x}"!
p.x = 44!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Another example: Binary tree
class BinaryTree!
!
def initialize(value = nil)!
@value = value!
@left = @right = nil!
end!
!
def insert(value)!
...!
end!
!
def traverse_in_order!
@left.traverse_in_order unless @left.nil?!
puts @value
unless @value.nil?!
@right.traverse_in_order unless @right.nil?!
end!
!
end!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Binary tree (cont.)
class BinaryTree!
!
!
def insert(value)!
if @value.nil?!
@value = value!
elsif value < @value!
if @left.nil?!
@left = BinaryTree.new(value)!
else !
@left.insert(value) !
end!
else!
if @right.nil?!
@right = BinaryTree.new(value)!
else !
@right.insert(value) !
end!
end!
end!
end!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Let’s play with our example
tree1 = BinaryTree.new(10)!
tree1.insert(5)!
tree1.insert(15)!
tree1.insert(20)!
!
tree1.traverse_in_order!
tree2 = BinaryTree.new!
input = %w{one two three four five six}!
!
for w in input!
"tree2.insert(w)!
end!
!
tree2.traverse_in_order!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS % notation
Modifier Meaning %q[] Non-­‐interpolated String (except for \\ \[ and \]) %Q[] Interpolated String (default) %r[] Interpolated Regexp (flags can appear aYer the closing delimiter) %i[] Non-­‐interpolated Array of symbols, separated by whitespace (aYer Ruby 2.0) %I[] Interpolated Array of symbols, separated by whitespace (aYer Ruby 2.0) %w[] Non-­‐interpolated Array of words, separated by whitespace %W[] Interpolated Array of words, separated by whitespace %x[] Interpolated shell command RUBY LUCIANO GARCÍA-­‐BAÑUELOS Arrays
x = Array.new
# same as x = []!
x << 10 "
" # same as x.push(10)!
!
x[0] = 99!
y = ["Alice", 23, 7.3]!
x[1] = y[1] + y[-1]!
From the end and downwards RUBY LUCIANO GARCÍA-­‐BAÑUELOS Iterating through arrays
a = [1,2,3,4,5]!
i = 0!
while i < a.length!
puts a[i]!
i = i + 1!
end!
a = [1,2,3,4,5]!
a.each { |x| puts x }!
Code block Delimited by: { … } or do … end Parameter list RUBY LUCIANO GARCÍA-­‐BAÑUELOS body More examples on code blocks
3.times { puts "hello"; puts "goodbye" }!
5.upto(10) { |x| puts(x + 1) }!
[1,2,3,4,5].find { |y| y % 2 == 0 }!
[5,4,3].collect { |x| -x }!
(1..10).inject(:*)!
◦  n.-mes runs code block n <mes ◦  n.upto(m) runs code block for integers n..m ◦  a.find returns first element x of array such that the block returns true for x ◦  a.collect applies block to each element of array and returns new array (a.collect! modifies the original)‫ ‏‬ RUBY LUCIANO GARCÍA-­‐BAÑUELOS Calling code blocks
def countx(x)‫!‏‬
for i in (1..x)‫!‏‬
puts i!
yield!
end!
end!
!
countx(4) { puts "foo" }!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS >> countx(4) 1 foo 2 foo 3 foo 4 foo => 1..4 Let’s improve our binary tree
class
class BinaryTree!
!
def traverse(mode = :in_order, &block)!
case mode!
when :in_order!
@left.traverse mode, &block unless @left.nil?!
yield @value!
@right.traverse mode, &block unless @right.nil?!
when :pre_order!
...!
when :post_order!
...!
end!
end!
!
end!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Let’s play again with our
example
tree1 = BinaryTree.new!
[10,20,15,5].each {|x|
tree1.insert(x)}!
tree1.traverse { |x| puts x }!
tree2 = BinaryTree.new!
%w{one two three four five six}.each{ |w| tree2.insert(w) }!
!
tree2.traverse(:in_order) { |x| print " #{x}" }; puts!
tree2.traverse(:pre_order) { |x| print " #{x}" }; puts!
tree2.traverse(:post_order) { |x| print " #{x}" }; puts!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Hashes
person = Hash.new"# same as person = {}!
!
person["last_name"] = "Rodriguez"!
person[:first_name] = "Alice"!
order = {"item" => "Corn Flakes", "weight" => 18}!
order = {:item => "Corn Flakes", :weight => 18}!
order = {item: "Corn Flakes", weight: 18}!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Regular Expressions
•  A way of describing pamerns or sets of strings ◦  Searching and matching ◦  Formally describing strings ◦  The symbols (lexemes or tokens) that make up a language •  Common to lots of languages and tools ◦  awk, sed, perl, grep, Java, OCaml, C libraries, etc. •  Based on some really elegant theory ◦  We’ll see that soon Ruby Luciano García-­‐Bañuelos Example Regular Expressions in
Ruby
•  /Ruby/ ◦  Matches exactly the string "Ruby" ◦  Regular expressions can be delimited by /’s ◦  Use \ to escape /’s in regular expressions •  /(Ruby|OCaml|Java)/ ◦  Matches either "Ruby", "OCaml", or "Java" •  /(Ruby|Regular)/ or /R(uby|egular)/ ◦  Matches either "Ruby" or "Regular" ◦  Use ()’s for grouping; use \ to escape ()’s Ruby Luciano García-­‐Bañuelos Repetition in Regular
Expressions
•  /(Ruby)*/ ◦  {"", "Ruby", "RubyRuby", "RubyRubyRuby", ...} ◦  * means zero or more occurrences •  /(Ruby)+/ ◦  {"Ruby", "RubyRuby", "RubyRubyRuby", ... } ◦  + means one or more occurrence ◦  so /e+/ is the same as /ee*/ Ruby Luciano García-­‐Bañuelos Repetition in Regular
Expressions
• /(Ruby)?/ ◦  {"", "Ruby"} ◦  ? means op,onal, i.e., zero or one occurrence • /(Ruby){3}/ ◦  {“RubyRubyRuby”, “RubyRubyRubyRuby”, …} ◦  {x} means repeat the search for at least x occurrences • /(Ruby){3, 5}/ ◦  {“RubyRubyRuby”, “RubyRubyRubyRuby”, “RubyRubyRubyRubyRuby”} ◦  {x, y} means repeat the search for at least x occurrences and at most y occurrences Ruby Luciano García-­‐Bañuelos Watch Out for Precedence
•  /(Ruby)*/ means {"", "Ruby", "RubyRuby", ...} ◦  But /Ruby*/ matches {"Rub", "Ruby", "Rubyy", ...} •  In general ◦  * {n} and + bind most <ghtly ◦  Then concatena<on (adjacency of regular expressions)‫ ‏‬ ◦  Then | •  Best to use parentheses to disambiguate Ruby Luciano García-­‐Bañuelos Character Classes
•  /[abcd]/ ◦  {"a", "b", "c", "d"} (Can you write this another way?)‫ ‏‬ •  /[a-­‐zA-­‐Z0-­‐9]/ ◦  Any upper or lower case lemer or digit •  /[^0-­‐9]/ ◦  Any character except 0-­‐9 (the ^ is like not and must come first)‫ ‏‬ •  /[\t\n ]/ ◦  Tab, newline or space •  /[a-­‐zA-­‐Z_\$][a-­‐zA-­‐Z_\$0-­‐9]*/ ◦  Java iden<fiers ($ escaped...see next slide)‫ ‏‬ Ruby Luciano García-­‐Bañuelos Special Characters
. ^ any character beginning of line $ \$
end of line just a $ \d
digit, [0-­‐9] \s \w
whitespace, [\t\r\n\f] word character, [A-­‐Za-­‐z0-­‐9_] \D
\S
non-­‐digit, [^0-­‐9] non-­‐space, [^\t\r\n\f] \W non-­‐word, [^A-­‐Za-­‐z0-­‐9_] Ruby Luciano García-­‐Bañuelos Potential Character Class Confusions
^ inside character classes: not
outside character classes: beginning of line [] inside regular expressions: character class outside regular expressions: array note: [a-­‐z] does not make a valid array, () inside character classes: literal characters ( )‫ ‏‬ /(0..2)/ does not mean 012 outside character classes: used for grouping -  inside character classes: range (e.g., a to z given by [a-­‐z])‫ ‏‬ outside character classes: dash Ruby Luciano García-­‐Bañuelos Using regular expressions
line = gets
if line =~ /Ruby/ then
puts "Found Ruby"!
end!
gets =~ /^Min: (\d+)
min, max = $1, $2!
# read line from standard input!
# returns nil if not found!
Max: (\d+)$/!
def m(s)‫!‏‬
s =~ /(Foo)/!
puts $1
# prints Foo!
end!
m("Foo")‫!‏‬
puts $1
# prints nil!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS Finally … metaprogramming
class Polyglot!
def initialize!
@@greetings = {estonian: "Tere hommikust", english: "Good morning"}!
end!
def add_language(language, greeting)!
@@greetings[language] = greeting if language.is_a? Symbol!
end!
def method_missing(name)!
unless @@greetings[name].nil?!
puts @@greetings[name]!
else!
super!
end!
end!
end!
!
a = Polyglot.new!
!
a.estonian!
a.english!
RUBY LUCIANO GARCÍA-­‐BAÑUELOS