From: billtj@... (Bill Tj)
Date: 2002-10-08T00:12:31+09:00
Subject: Things That Newcomers to Ruby Should Know

Hi,

I have also updated the list at
http://www.glue.umd.edu/~billtj/ruby.html, which is the HTML version
of the list below.

I am sorry that our NNTP server was down since last Thursday morning
(10/3/02) and even until now they are still working on it.  So I will
be "crippled" for a while and will not be able to follow the
discussions in almost real time (as the Google groups is about 30
minutes to one hour delay (?) as compared to the "tin" reader that I
use.)  I have not seen many e-mails either, so probably our email
server is also affected.

In particular, it seems that the Google poster does not really support
80 column (or around that number) text, so some of the lines below are
wrapped around, which make them harder to read.

Regards,

Bill
=============================================================================
                   Things That Newcomers to Ruby Should Know

   [1]Plain Text Format
     * Resources:
          + HOME PAGE: [2]http://www.ruby-lang.org/en/
          + FAQ: [3]http://www.rubycentral.com/faq/
          + PITFALL:
            [4]http://rwiki.jin.gr.jp/cgi-bin/rw-cgi.rb?cmd=view;name=pit
            fall
          + ONLINE TUTORIAL/DOC/BOOK:
[5]http://www.rubycentral.com/book/
          + VERY USEFUL HINTS:
               o "Programming Ruby" book by David Thomas and Andrew
Hunt,
                 "When Trouble Strikes" Chapter, "But It Doesn't Work"
                 Section
               o "The Ruby Way" book by Hal Fulton, Chapter 1: "Ruby
In
                 Review"

    1. Use "ruby -w" instead of simply "ruby" to get helpful warnings.
If
       not invoking "ruby" directly, you can set the environment
variable
       RUBYOPT to 'w':
          + win32:
            C:\> set RUBYOPT=w
                or
            pressing F5 (to execute) in the Scite editor will give you
warnings
            (and F4 will position at problematic line).
          + unix:
            sh# export RUBYOPT="w"
                or
            csh# setenv RUBYOPT "w"
    2. The notation "Klass#method" in documentation is used only to
       represent an "instance method" of an object of class Klass; it
is
       not a Ruby syntax at all. A "class method" in documentation, on
       the other hand, is usually represented as "Klass.method" (which
is
       a valid Ruby syntax).
    3. Be aware of the lexical scoping interaction between local
       variables and block local variables. If a local variable is
       already defined before the block, then the block will use (and
       quite possibly modify) the local variable; in this case the
block
       does not introduce a new scope. Example:
            (0..2).each do |i|
              puts "inside block: i = #{i}"
            end
            puts "outside block: i = #{i}"    # >> undefined `i'
       On the other hand,
            i = 0
            (0..2).each do |i|
              puts "inside block: i = #{i}"
            end
            puts "outside block: i = #{i}"    # >> 'outside block: i =
2'
       and
            j = 0
            (0..2).each do |i|
              j = i
            end
            puts "outside block: j = #{j}"    # >> 'outside block: j =
2'
    4. The String#[Fixnum] method does not return the "character"
(which
       is a string of length one) at the Fixnum position, but instead
the
       ASCII character code at the position (however, this may change
in
       the future). Currently, to get the character itself, use
       String#[Fixnum,1] instead.
       Furthermore, there are additional ASCII conversion methods such
as
          + Integer#chr to convert from the ASCII code to the
character
            65.chr    # >> "A"
          + ?char to convert from the character to the ASCII code
            ?A    # >> 65
    5. In Ruby, there are two sets of logical operators: [!, &&, ||]
and
       [not, and, or]. [!, &&, ||]'s precedence is higher than the
       assignments (=, %=, ~=, /=, etc.) while [not, and, or]'s
       precedence is lower. Also note that while &&'s precedence is
       higher than ||'s, the and's precedence is the same as the or's.
    6. In the case statement
            case obj
            when obj_1
              ....
            when obj_k
              ....
       it is the "===" method which is invoked, not the "==" method.
       Also, the order is "obj_k === obj" and not "obj === obj_k".
       The reason for this order is so that the case statement can
       "match" obj in more flexible ways. Three interesting cases are
       when obj_k is either a Module/Class, a Regexp, or a Range:
          + The Module/Class class defines the "===" method as a test
            whether obj is an instance of the module/class or its
            descendants ("obj#kind_of? obj_k").
          + The Regexp class defines the "===" method as a test
whether
            obj matches the pattern ("obj =~ obj_k").
          + The Range class defines the "===" method as a test whether
            obj is an element of the range ("obj_k.include? obj").
    7. Array.new(2, Hash.new) # >> [{}, {}]
       but the two array elements are identical objects, not
independent
       hashes.
    8. After reading data from a file and putting them into variables,
       the data type is really String. To convert them into numbers,
use
       the "to_i" or "to_f" methods. If, for example, you use the "+"
       operator to add the "numbers" without calling the conversion
       methods, you will simply concatenate the strings.
       An alternative is to use "scanf"
       ([6]http://www.rubyhacker.com/code/scanf).
    9. It is advisable not to write some white space before the
opening
       '(' in a method call; else, Ruby with $VERBOSE set to true may
       give you a warning.
   10. The "dot" for method call is the strongest operator. So for
       example, while in some other languages the number after the dot
in
       a floating point number is optional, it is not in Ruby. For
       example, "1.e6" will try to call the method "e6" of the object
1
       (which is a Fixnum). You have to write "1.0e6".
       However, notice that although the dot is the strongest
operator,
       its precedence with respect to method name may be different
with
       different Ruby versions. At least in Ruby 1.6.7, "puts
       (1..3).length" will give you a syntax error; you should write
       "puts((1..3).length)" instead.
   11. Be careful when using "mutable" objects as hash keys. To get
the
       expected result, call Hash#rehash before accessing the hash
       elements. Example:
            s = "mutable"
            arr = [s]
            hsh = { arr => "object" }
            s.upcase!
            p hsh[arr] # >> nil (maybe not what was expected)
            hsh.rehash
            p hsh[arr] # >> "object"
   12. In Ruby, only false and nil are considered as false in a
Boolean
       expression. In particular, 0 (zero), "" or '' (empty string),
[]
       (empty array), and {} (empty hash) are all considered as true.
   13. There is no standard, built-in deep copy in Ruby. One way to
       achieve a similar effect is by serialization/marshalling.
Because
       in Ruby everything is a reference, be careful when you want to
       "copy" objects, especially for objects that contain other
objects
       (such as arrays and hashes) and when the containment is more
than
       one level deep.
   14. "0..k" represents a Range object, while "[0..k]" represents an
       array with a single element of type Range. For example, if
            [0..2].each do |i|
              puts "i = #{i}"
            end
       does not give what you expect, probably you should have written
            (0..2).each do |i|
              puts "i = #{i}"
            end
       or
            0.upto(2) do |i|
              puts "i = #{i}"
            end
       instead. Note also that Ruby does not have objects of type
"Tuple"
       (which are immutable arrays) and parentheses are usually put
       around a Range object for the purpose of precedence grouping
(as
       the "dot" is stronger than the "dot dot" in the above example).

Things That Are Good to Know :-)

    1. In Ruby the "self assignment operator" goes beyond "+=, -=, *=,
       /=, %=". In particular, operators such as "||=" also exist.
Please
       see Table 18.4 in the "Programming Ruby" book for the complete
       list.
    2. If you do extensive numerical computations, you may consider
using
       "Numerical Ruby"
       ([7]http://www.ir.isas.ac.jp/~masa/ruby/index-e.html).
    3. If you have numerical arrays which consume a large amount of
       memory and CPU time, you may consider using "NArray" which is
part
       of the Numerical Ruby
       ([8]http://www.ir.isas.ac.jp/~masa/ruby/na/SPEC.en).
    4. If you do integration between Ruby and C/C++, you may consider
       using "SWIG" ([9]http://www.swig.org/).
    5. If you do a lot of translation from Ruby to C, you may consider
       using "rb2c"
       ([10]http://easter.kuee.kyoto-u.ac.jp/~hiwada/ruby/rb2c/).
    6. If you want to speed up some parts of your Ruby code by writing
       them in C, you may consider using "Inline"
       ([11]http://sourceforge.net/projects/rubyinline/).

     * For comments on this list, you may e-mail me directly at
       [12]billtj@glue.umd.edu.
     _________________________________________________________________

   Last updated: Oct 7, 2002.
   This list itself is available at
   [13]http://www.glue.umd.edu/~billtj/ruby.html.
   The plain text format is produced from the HTML format with "lynx
   -dump".
     _________________________________________________________________

References

   1. file://localhost/.automount/tulsi/home/tjb/Conf/ruby.txt
   2. http://www.ruby-lang.org/en/
   3. http://www.rubycentral.com/faq/
   4. http://rwiki.jin.gr.jp/cgi-bin/rw-cgi.rb?cmd=view;name=pitfall
   5. http://www.rubycentral.com/book/
   6. http://www.rubyhacker.com/code/scanf
   7. http://www.ir.isas.ac.jp/~masa/ruby/index-e.html
   8. http://www.ir.isas.ac.jp/~masa/ruby/na/SPEC.en
   9. http://www.swig.org/
  10. http://easter.kuee.kyoto-u.ac.jp/~hiwada/ruby/rb2c/
  11. http://sourceforge.net/projects/rubyinline/
  12. mailto:billtj@glue.umd.edu
  13. http://www.glue.umd.edu/~billtj/ruby.html