Seven Languages in Seven Weeks

This morning, after 10 minutes struggle of do or do not follow the self study section. Just spend several hours of searching, coding and debugging, finally I got the following ruby script that is able to pass the self study excise.

diff -r 9efeca9bd507 learning/ruby/acts_as_csv_module.rb
--- a/learning/ruby/acts_as_csv_module.rb   Tue Feb 07 15:13:11 2017 +0800
+++ b/learning/ruby/acts_as_csv_module.rb   Tue Feb 07 15:13:49 2017 +0800
@@ -1,32 +1,90 @@
 module ActsAsCsv
+
   def self.included(base)
     base.extend ClassMethods
   end
+
   module ClassMethods
+    
     def acts_as_csv
       include InstanceMethods
     end
+
+    def acts_as_enumerable
+      include Enumerable
+    end
   end
+
   module InstanceMethods
+    
     def read
       @csv_contents = []
       filename = self.class.to_s.downcase + '.txt'
       file = File.new(filename)
-      @headers = file.gets.chomp.split(', ' )
+      CsvRow.headers = file.gets.chomp.split(', ' )
+
+      # puts "CsvRow.headers is #{CsvRow.headers}"
       file.each do |row|
-        @csv_contents << row.chomp.split(', ' )
+        csvrow = CsvRow.new
+        csvrow.row_content = row.chomp.split(', ' )
+
+        # puts "csvrow is #{csvrow.row_content}"
+   @csv_contents << csvrow
       end
     end
-    attr_accessor :headers, :csv_contents
+    
+    attr_accessor :csv_contents
+    
     def initialize
       read
     end
+
+    def each(&block)
+      # puts "csv_contents.each is #{@csv_contents.each}"
+      @csv_contents.each(&block)
+    end
+    
   end
 end
+
 class RubyCsv # no inheritance! You can mix it in
   include ActsAsCsv
   acts_as_csv
+  acts_as_enumerable
 end
-m = RubyCsv.new
-puts m.headers.inspect
-puts m.csv_contents.inspect
+
+class CsvRow
+  @@header_indexes = {}
+  
+  def method_missing name, *args
+    @row_content[@@header_indexes[name.to_s]]
+  end
+
+  attr_accessor :row_content
+
+  def initialize
+    @row_content = []
+  end
+
+  def self.headers=(h)
+    @@headers = h
+
+    # puts "h is #{h}"
+    h.each_index {|i| @@header_indexes[h[i]] = i}
+    # puts "@@header_indexes is #{@@header_indexes}"
+  end
+
+  def self.headers
+    @@headers
+  end
+end
+
+
+# m = RubyCsv.new
+# puts m.headers.inspect
+# puts m.csv_contents.inspect
+
+csv = RubyCsv.new
+
+# puts "csv_contents is #{csv.csv_contents}"
+csv.each {|row| puts row.one}

Ruby feature learned

1. Class variable is defined and accessed with “double at” prefix @@.
2. Class accessor must be defined with self. prefix, otherwise the result method will be instance accessor, I was confused by the complex syntax sugar used in the link.
3. Array has convenient .each_index method that will save you lots of type.
4. each method have to be defined as each(&block) to be able to work, and the inside each being invoked should also be invoked as .each(&block) for the block to be passed into it.
5. attr_accessor will generate ruby specific getter and setters codes for decorated attributes(have to be specified in the form of :rubysymbol).