Ruby 1.9 porting tips/notes

April 15, 2008
  1. formal argument cannot be an instance variable:
    In ruby1.8 it’s possible to use an instance variable as a block argument:

    class Foo
      attr_accessor :bar
      def test
         [1,2,3].each {|@bar| }
         # @bar will be 3 here
      end
    end
    

    This no longer works in ruby1.9, you as it always creates a new local variable block argument. The equivalent in ruby1.9:

    class Foo
      attr_accessor :bar
      def test
         [1,2,3].each {|bar| @bar=bar }
         # @bar will be 3 here
      end
    end
    
  2. warning: shadowing outer local variable:
    In ruby1.9 the block arguments are always local to block, in ruby1.8 if there’s an existing variable with the same name, the block parameter will use that one:  

    i = 0
    [1,2,3].each {|i| }
    puts i
    

    This will print 0 in ruby1.9, as the variables named i inside/outside the block are different, and 3 in ruby1.8, as here the block reuses the outside variable i.

    As with most warning, this warning doesn’t means that your code is incorrect, only that it might be incorrect.
    For example the code bellow works the same in ruby1.9 and 1.8:

    options = options.inject({}) do |options,pair|
      options[pair.first.to_sym] = pair.last.to_sym; options
    end
    

    It still makes sense to rewrite the above code just to supress warnings.

    Note: You should set RUBYOPT to -w, or start your program with ruby -w, for this warning to show up

  3. syntax error, unexpected ‘,’, expecting tASSOC
    ruby1.8 supports , in hash definition, in 1.9 you have to use =>.  

    So the following valid ruby1.8:

    {"a","b"}
    

    has to be rewritten in ruby1.9:

    {"a" => "b"}
    
  4. invalid multibyte char:
    the default encoding in ruby 1.9 for files is US-ASCII, if you have a non ASCII character in your text file you have to specify the encoding of the source code. You can do it by adding the following line to your ruby file:  

    # coding:utf-8
    
  5. NoMethodError: undefined method `to_a’ for “…”:String:
    In Ruby1.8 the String class has a to_a method, so in ruby1.8 you can write:

    lines = string.to_a
    

    The equivalent in ruby1.9 is:

    lines = string.lines.to_a
    # chars = string.chars.to_a # to get array of chars
    # bytes = string.bytes.to_a # to get array of bytes
    

    The issue with this solution, is that the ruby1.9 solution is not compatible with ruby1.8.

    Some ideas for a ruby1.9 and ruby1.8 compatible solution:

    The first one is to add a lines method to the String, so you can use the ruby1.9 syntax:

    unless String.method_defined?(:lines) then
      class String
        def lines
          to_a
        end
      end
    endif
    

    The downside is that this lines method is not 100% compatible with ruby1.9 String#lines – for example string.lines(“\n\r”) won’t work. 

    The second one is to check at each call whether it has the lines method:

    if str.respond_to?(:lines) then
      lines = string.lines.to_a
    else
      lines = string.to_a
    end
    
  6. unexpected ‘:’, expecting keyword_then or ‘,’ or ‘;’ or ‘\n’:
    case or if with : instead of then  

    Ruby1.8 allows the use of : shortcut instead of then in if and case expressions. In Ruby1.9 this is no more allowed.

    case 'test'
      when 'test': print 'OK'
    end
    

    In ruby1.9 you’ll get a syntax error, so you have to replace the ‘:’ with ‘then’

    case 'test'
      when 'test' then print 'OK'
    end
    
  7. no such file to load — base64:
    require "base64": ruby 1.9 ships without base64. You should use Array#pack, unpack  

     require 'base64'
     enc = Base64.encode64('Send reinforcements')
     plain = Base64.decode64(enc)
    

    In ruby1.9 you can write:

    enc = ['Send reinforcements'].pack( 'm' )
    plain = enc.unpack( 'm' )[0]
    
  8. ‘struct RString’ has no member named ‘ptr’
    ‘struct RString’ has no member named ‘len’:
    In ruby1.9 for the RString in C extensions was changed because of optimization, you should use the RSTRING_LEN, RSTRING_PTR macros instead of directly accessing the len, ptr members.  

    len = RSTRING(foo)->len
    ptr = RSTRING(foo)->ptr
    

    Should be changed to

    len = RSTRING_LEN(foo);
    ptr = RSTRING_PTR(foo);
    
  9. .methods changed from Strings to Symbols
    The contents of the methods array was changed from String to Symbol, so if you were doing something like this in ruby1.8:

    Object.methods.include?("to_s")
    

    The ruby1.9 version is:

    Object.methods.include?(:to_s)
    

    And the following works in ruby1.8 and 1.9:

    object.respond_to?(:some_method)
    
  10. TypeError: cannot assign nil; use Hash#delete instead
    In ruby1.8 you can remove an environment variable by setting it to nil.
    In ruby1.9 use the delete method instead:

    ENV.delete('MY_ENV_VARIABLE')
    

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