The Ruby Test

[wtd]

Test #1

Please private message me with your answers. I'll post a list of those who've successfully completed the test, which, for those who are curious, is a score of 125 points, with at least one 20 point question answered successfully.

1. Explain the differences between:
   
   

   code:

   name $name @name @@name NAME

   
   
   5 points
   
   
2. Explain the significance of ! and ? as suffixes on method names.
   
   5 points
   
   
3. Consider the following snippet from irb:
   
   

   code:

   irb(main):001:0> class Foo irb(main):002:1>    private irb(main):003:1>    def bar irb(main):004:2>      "baz" irb(main):005:2>    end irb(main):006:1> end => nil irb(main):007:0> Foo.new.bar NoMethodError: private method `bar' called for #<Foo:0x2dc0568>         from (irb):7

   
   
   Call the bar method on a Foo object regardless of the "private" modifier.
   
   10 points
   
   
4. Explain the differences between public, private, and protected.
   
   5 points
   
   
5. Explain how the public, private, and protected modifiers work in Ruby. How can the following make both the bar and baz methods private?
   
   

   code:

   class Foo    private    def bar       "bar"    end        def baz       "baz"    end end

   
   
   20 points
   
   
6. Explain how Ruby makes it possible for a method defined outside of a class to be used inside a class.
   
   

   code:

   def bar    "bar" end class Foo    def baz       bar    end end

   
   
   10 points
   
   
7. a) Explain why an object, even if it "is a" Enumerable, cannot be guaranteed to have a working "collect" method.
   
   5 points
   
   b) Demonstrate how to check to make sure an object does have a working "collect" method.
   
   5 points
   
   
8. Explain what the ternary operator is, and how it can be useful.
   
   5 points
   
   
9. Write a program which reads through a simple plain text log file. The log file is in CSV format and each record contains, in this order: the filename, the date as the number of seconds since epoch, and the name of the user who made the request.
   
   The program should print this information to the console, but with the time in a human-readabe format.
   
   Assume the log file can be of any length. Make your program reasonably memory efficient.
   
   10 points
   
   
10. Consider the following method:
    
    

    code:

    $correct_answer = 42 def guess(number_of_guesses = 3)    user_guess = gets.to_i        if user_guess == $correct_answer       puts "Correct!"    else       raise "Wrong..."    end end

    
    
    Modify this method so that:
    
    
    
    
    • The exception never escapes the method.
      
    • The user is only allowed to guess at most the number of times indicated by the method's parameter.
      
    • The current body of the method is left intact.
      
    
    
    10 points
    
    
11. Aside from a bit shift, what would you use the << operator for in Ruby?
    
    5 points
    
    
12. Write code that opens a file for appending and reading.
    
    5 points
    
    
13. Without seeing the code that created a range "foo", write a line of code which determines whether or not the range was created with ".." or "...".
    
    5 points
    
    
14. Consider the hash:
    
    

    code:

    baz = {"foo" => "bar"}

    
    
    Explain what changes would be necessary to make:
    
    

    code:

    baz["fOO"]

    
    
    Return "bar".
    
    The changes may not affect other hashes in the same program.
    
    10 points
    
    
15. Consider the following:
    
    

    code:

    irb(main):001:0> arr = [54, 67, 23, 42, 27, 98, 12, 84] => [54, 67, 23, 42, 27, 98, 12, 84] irb(main):002:0> arr.values_at(1, 3, 5) => [67, 42, 98]

    
    
    Let's assume arr is some arbitrary length, greater than 10,000 elements. Write a reasonably concise bit of code which uses the values_at method to retrieve only the elements at even indexes.
    
    10 points
    
    
16. Let's say we have a plain text data file that has information about people stored as "key=value" pairs separated by commas.
    
    Each record should be parsed into a hash.
    
    

    code:

    def parse_record(line)    record = {}    line.split(/\s*,\s*/).each do |pair|       key, pair = pair.split(/\s*=\s*/, 2)       record[key] = pair    end    record end

    
    
    Modify this to provide significantly better memory efficiency for large datasets.
    
    10 points
    
    
17. Take a name class:
    
    

    code:

    class Name    def initialize(first, last)       @first, @last = first, last    end end

    
    
    Make it a valid Enumerable object.
    
    5 points
    
    
18. Modify the Array class so that when a new value is pushed (with the push method) onto the end of the array, certain actions are carried out.
    
    These actions should be specified at run-time for a given Array object by an "on_push" method you create. The "actions" should be aware of the arguments being provided to "push".
    
    20 points
    
    
19. Add a "reverse" method to the Enumerable module which outputs an Array. Implement your reverse method using only the "inject" method.
    
    Test it with:
    
    

    code:

    class Foo    include Enumerable        def each       yield 42       yield 27    end end

    
    
    Calling:
    
    

    code:

    Foo.new.reverse

    
    
    Should return:
    
    

    code:

    [27, 42]

    
    
    10 points
    
    

[octopi]

...Since its been 8 months would you consider starting to post some anwsers the the questions?