Ruby. A Very Brief Introduction. Andreas Klappenecker

Transcription

1 Ruby A Very Brief Introduction Andreas Klappenecker

2 Ruby Ruby is a very popular open source interpreted programming language. Ruby combines object-oriented programming with concepts from functional programming languages. The language is dynamically typed, flexible, and very expressive.

3 Getting Ruby Ruby is available for Windows, Linux, OS X, see It comes by default with many Linux and OS X operating systems (install Xcode). It is installed on unix.cse.tamu.edu If you want to use it from your smartphone or touchscreen computer without installing it, then a slow but functional online version is available at

4 Getting Started Start the interactive ruby interpreter irb You can experiment with the language constructs.

5 Objects and their Classes Everything (well, almost everything) is an object in Ruby. You can find out the class of an object obj by invoking the method obj.class >> 4.class => Fixnum >> "123".class => String >> '123'.class => String

6 Listing the Available Methods >> 4.methods.sort => ["%", "&", "*", "**", "+", "-", "/", "<", "<<", "<=", "<=>", "==", "===", "=~", ">", ">=", ">>", "[]", "^", " id ", " s ", "abs", "between?", "ceil", "chr", "class", "clone", "coerce", "denominator", "display", "div", "divmod", "downto", "dup", "enum_for", "eql?", "equal?", "even?", "ext", "fdiv", "floor", "freeze", "frozen?", "gcd", "gcdlcm", "hash", "id", "id2name", "inspect", "instance_eval", "instance_exec", "instance_of?", "instance_variable_defined?", "instance_variable_get", "instance_variable_set", "instance_variables", "integer?", "is_a?", "kind_of?", "lcm", "method", "methods", "modulo", "next", "nil?", "nonzero?", "numerator", "object_id", "odd?", "ord", "power!", "prec", "prec_f", "prec_i", "pred", "private_methods", "protected_methods", "public_methods", "quo", "rdiv", "remainder", "respond_to?", "round", "rpower", "s", "singleton_method_added", "singleton_methods", "size", "step", "succ", "taguri", "taguri=", "taint", "tainted?", "tap", "times", "to_a", "to_enum", "to_f", "to_i", "to_int", "to_r", "to_s", "to_sym", "to_yaml", "to_yaml_properties", "to_yaml_style", "truncate", "type", "untaint", "upto", "zero?", " ", "~"]

7 Data Types Integer: 1,2,-1,10**1000 Float: 2.1, Array: a = [1,2,3] Range: String: abc Adding yields #{1+2} # String interpolation abc # single quotes do not allow string interpolation Symbol: :name # similar to name but cannot be mutated Hash: { :name => George, :age => 12 } puts h[:name] # prints George

8 Variables Ruby is dynamically typed, so you do not have to declare your variables. There is some punctuation that allow you to identify the scope of a variable var # lower case variables are local # variables starting are instance variables # same scope as self $var # global variables

9 Creating Classes class Person attr_accessor :name, :age def full_info return is years old" p = Person.new; p.name = George ; p.age = 12 puts p.full_info # prints George is 12 years old

10 Enumerable Module Ruby does have for-loops and similar constructs. However, it is more common to use methods from the Enumerable module. [1,2,3].each { number puts 2*number } [1,2,3].any? { number number.even? } [2,4,6].all? { number number.even? } [1,2,3].map { x x**2 } # create array with squared elems [1,2,3].inject(:+) [1,2,3].inject(:*) # add all elements of the array # multiply all elements of the array

11 Exting Existing Classes # The class Integer does not contain a method to compute # factorials. We can simply re-open the class and define # the missing method. This method works for positive integers. class Integer def factorial (1..self).inject(:*)

12 Comments Everything after a # is a comment You can comment out larger portions by enclosing text in =begin = The equality signs need to be at the beginning of the line.

13 Convert len LSBs into Array # Given an integer such as n=15, the method # n.to_a(5) determines the 5 least significant bits of n # and collects them in an array class Integer def to_a( len ) (1..len).map { x (self & 2**(len - x)) > 0 }

14 Unnamed Functions neg_op = Proc.new { a!a } and_op = Proc.new { a,b a&b } or_op = Proc.new { a,b a b } xor_op = Proc.new { a,b a^b } conditional_op = Proc.new { a,b!a b } equivalence_op = Proc.new { a,b a.eql?(b) }

15 Printing a Truth Table class Proc def truth_table len = self.arity (2**len).times do x arg = x.to_a(len) print arg.join("\t") + "\t: #{(self.call(*arg)).to_s}\n"