1. Ruby
A quick Ruby Tutorial
• Invented by Yukihiro Matsumoto, “Matz”
• 1995
• Fully object-oriented
COMP313
Source: Programming Ruby, The Pragmatic • alternative to Perl or Python
Programmers’ Guide by Dave Thomas, Chad
Fowler, and Andy Hunt
How to run Simple method example
• Command line: ruby <file> def sum (n1, n2)
n1 + n2
• Interactive: irb
end
• Resources: sum( 3 , 4) => 7
– see web page sum(“cat”, “dog”) => “catdog”
– man ruby
load “fact.rb”
fact(10) => 3628800
executable shell script Method calls
#!/usr/bin/ruby "gin joint".length 9
print “hello worldn” "Rick".index("c") 2
-1942.abs 1942
or better: #!/usr/bin/env ruby
make file executable: chmod +x file.rb Strings: ‘asn’ => “asn”
x=3
y = “x is #{x}” => “x is 3”
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2. Another method definition Name conventions/rules
def say_goodnight(name) • local var: start with lowercase or _
"Good night, #{name}" • global var: start with $
end • instance var: start with @
puts say_goodnight('Ma') • class var: start with @@
• class names, constant: start uppercase
following: any letter/digit/_ multiwords
produces: Good night, Ma either _ (instance) or mixed case
(class), methods may end in ?,!,=
Naming examples Arrays and Hashes
• local: name, fish_and_chips, _26 • indexed collections, grow as needed
• global: $debug, $_, $plan9 • array: index/key is 0-based integer
• hash: index/key is any object
• instance: @name, @point_1
a = [ 1, 2, “3”, “hello”]
• class: @@total, @@SINGLE,
a[0] => 1 a[2] => “3”
• constant/class: PI, MyClass, a[5] => nil (ala null in Java, but proper Object)
FeetPerMile
a[6] = 1
a => [1, 2, “3”, “hello”, nil, nil, 1]
Hash examples Control: if example
inst = { “a” => 1, “b” => 2 } if count > 10
inst[“a”] => 1 puts "Try again"
inst[“c”] => nil
elsif tries == 3
inst = Hash.new(0) #explicit new with default 0
instead of nil for empty slots puts "You lose"
inst[“a”] => 0 else
inst[“a”] += 1 puts "Enter a number"
inst[“a”] => 1 end
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3. Control: while example nil is treated as false
while weight < 100 and num_pallets <= 30 while line = gets
pallet = next_pallet() puts line.downcase
weight += pallet.weight end
num_pallets += 1
end
builtin support for Regular
Statement modifiers
expressions
• useful for single statement if or while /Perl|Python/ matches Perl or Python
• similar to Perl /ab*c/ matches one a, zero or more bs and
one c
• statement followed by condition:
/ab+c/ matches one a, one or more bs and one
c
puts "Danger" if radiation > 3000 /s/ matches any white space
/d/ matches any digit
square = 2 /w/ characters in typical words
square = square*square while square < 1000 /./ any character
(more later)
more on regexps Code blocks and yield
if line =~ /Perl|Python/ def call_block
puts "Scripting language mentioned: #{line}" puts "Start of method"
end yield
yield
puts "End of method"
line.sub(/Perl/, 'Ruby') # replace first 'Perl' with 'Ruby'
end
line.gsub(/Python/, 'Ruby') # replace every 'Python' with 'Ruby’
call_block { puts "In the block" } produces:
# replace all occurances of both ‘Perl’ and ‘Python’ with ‘Ruby’ Start of method
line.gsub(/Perl|Python/, 'Ruby') In the block
In the block
End of method
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4. parameters for yield Code blocks for iteration
def call_block animals = %w( ant bee cat dog elk ) # create an array
yield("hello",2) # shortcut for animals = {“ant”,”bee”,”cat”,”dog”,”elk”}
end animals.each {|animal| puts animal } # iterate
produces:
then ant
bee
cat
call_block { | s, n | puts s*n, "n" } prints
dog
hellohello
elk
Implement “each” with “yield” More iterations
# within class Array... [ 'cat', 'dog', 'horse' ].each {|name| print name, "
"}
def each
5.times { print "*" }
for every element # <-- not valid Ruby
3.upto(6) {|i| print i }
yield(element) ('a'..'e').each {|char| print char }
end [1,2,3].find { |x| x > 1}
end (1...10).find_all { |x| x < 3}
I/O leaving the Perl legacy behind
• puts and print, and C-like printf: while gets
printf("Number: %5.2f,nString: %sn", 1.23, if /Ruby/
"hello") print
#produces: end
Number: 1.23, end
String: hello
#input ARGF.each {|line| print line if line =~ /Ruby/ }
line = gets
print line print ARGF.grep(/Ruby/)
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5. Classes override to_s
class Song s.to_s => "#<Song:0x2282d0>"
def initialize(name, artist, duration)
@name = name class Song
@artist = artist def to_s
@duration = duration "Song: #@name--#@artist (#@duration)"
end end
end end
song = Song.new("Bicylops", "Fleck", 260) s.to_s => "Song: Bicylops--Fleck (260 )”
Some subclass supply to_s for subclass
class KaraokeSong < Song class KaraokeSong < Song
# Format as a string by appending lyrics to parent's to_s value.
def initialize(name, artist, duration, lyrics)
def to_s
super(name, artist, duration) super + " [#@lyrics]"
@lyrics = lyrics end
end end
end song.to_s "Song: My Way--Sinatra (225) [And now, the...]"
song = KaraokeSong.new("My Way", "Sinatra",
225, "And now, the...")
song.to_s "Song: My Way--Sinatra (225)"
Accessors
class Song
def name
@name
end
end
s.name => “My Way”
# simpler way to achieve the same
class Song
attr_reader :name, :artist, :duration
end
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