No variable declara<ons. sum = 0! i = 1! while i <= 10 do! sum += i*i! i = i + 1! end! print "Sum of squares is #{sum}\n"!

Transcription

1 Basic syntax No variable declara<ons sum = 0 i = 1 while i <= 10 do sum += i*i i = i + 1 print "Sum of squares is #{sum}\n" Newline is statement separator do end instead of { } Parenthesis are op<onal in method calls String interpola-on

2 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"

3 Variable names and scopes foo Local variable $foo Global Instance variable in object Class variable MAX_USERS Constant (by conven<on)

4 Ruby statements if x < 10 then... elsif x < else... while x < 10 do... Literal arrays array = [22, 34, 46, 92] for value in array do...

5 Ruby classes class Point def initialize(x, = = y def def = value p = Point.new(3,4) puts "p.x is #{p.x}" p.x = 44

6 Another example: Binary tree class BinaryTree def initialize(value = = = nil def insert(value)... def unless

7 Binary tree (cont.) class BinaryTree def = value elsif value if = BinaryTree.new(value) = BinaryTree.new(value)

8 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) tree2.traverse_in_order

9 % notation Modifier Meaning %q[] Non- interpolated String (except for \\ \[ and \]) %Q[] %r[] %i[] %I[] %w[] %W[] %x[] Interpolated String (default) Interpolated Regexp (flags can appear ayer the closing delimiter) Non- interpolated Array of symbols, separated by whitespace (ayer Ruby 2.0) Interpolated Array of symbols, separated by whitespace (ayer Ruby 2.0) Non- interpolated Array of words, separated by whitespace Interpolated Array of words, separated by whitespace Interpolated shell command

10 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

11 Iterating through arrays a = [1,2,3,4,5] i = 0 while i < a.length puts a[i] i = i + 1 a = [1,2,3,4,5] a.each { x puts x } Code block Delimited by: { } or do end Parameter list body

12 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 ( original returns new array (a.collect modifies the

13 Calling code blocks ( countx(x def ( 1..x ) for i in puts i yield countx(4) { puts "foo" } >> countx(4) 1 foo 2 foo 3 foo 4 foo => 1..4

14 Let s improve our binary tree class class BinaryTree def traverse(mode = :in_order, &block) case mode when mode, &block yield mode, &block when :pre_order... when :post_order...

15 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

16 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}

17 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

18 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

19 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

20 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

21 Watch Out for Precedence /(Ruby)*/ means {"", "Ruby", "RubyRuby",...} But /Ruby*/ matches {"Rub", "Ruby", "Rubyy",...} In general * {n} and + bind most <ghtly ( expressions Then concatena<on (adjacency of regular Then Best to use parentheses to disambiguate Ruby Luciano García- Bañuelos

22 Character Classes /[abcd]/ (? way {"a", "b", "c", "d"} (Can you write this another /[a- za- Z0-9]/ Any upper or lower case lemer or digit /[^0-9]/ ( first Any character except 0-9 (the ^ is like not and must come /[\t\n ]/ Tab, newline or space /[a- za- Z_\$][a- za- Z_\$0-9]*/ ( slide Java iden<fiers ($ escaped...see next Ruby Luciano García- Bañuelos

23 Special Characters. any character ^ beginning of line $ end of line \$ just a $ \d digit, [0-9] \s whitespace, [\t\r\n\f] \w word character, [A- Za- z0-9_] \D non- digit, [^0-9] \S non- space, [^\t\r\n\f] \W non- word, [^A- Za- z0-9_] Ruby Luciano García- Bañuelos

24 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, ( ( characters () inside character classes: literal /(0..2)/ does not mean 012 outside character classes: used for grouping ([ a- z ] - inside character classes: range (e.g., a to z given by outside character classes: dash Ruby Luciano García- Bañuelos

25 Using regular expressions line = gets # read line from standard input if line =~ /Ruby/ then # returns nil if not found puts "Found Ruby" gets =~ /^Min: (\d+) Max: (\d+)$/ min, max = $1, $2 ( m(s def s =~ /(Foo)/ puts $1 # prints Foo (" m("foo puts $1 # prints nil

26 Finally metaprogramming class Polyglot def initialize = {estonian: "Tere hommikust", english: "Good morning"} def add_language(language, greeting) = greeting if language.is_a? Symbol def method_missing(name) unless puts else super a = Polyglot.new a.estonian a.english