Category Archive for ‘programming’ at Ruby Blender

Archive for the 'programming' Category

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This is the first in a series of entries which I’m pulling over articles from an old blog, revising, etc…

The Problem

One of the neat things about Ruby is it’s ability to create accessor methods for you, by simply declaring attr_reader, attr_writer, or attr_accessor. However, there’s not an easy way to define a default value for an attribute. The original version of this code was based off of Create getter and setter on a valorized variable and ideas from Ruby Quiz #67: Metakoans. The main difference between it and Sandro Paganotti’s version is that you can pass in a block which will be evaluated each time it is invoked (in case the value might depend on something else). Additionally, it will work with boolean types.

The Solution

class Object def self.attribute(*arg,&block) (name, default) = arg short_name = name.to_s.sub(/\?/,"") self.send(:define_method, name) { if instance_variables.include? "@#{short_name}" self.instance_eval "@#{short_name}" else if block_given? instance_eval &block else default end end } self.send(:define_method, "#{short_name}="){ |value| self.instance_eval "@#{short_name} = value" } end end

In order to use it, you could do something like this:

class Foo attribute :bar attribute(:fud) {instance_variables.include?("@bar") ? @bar : ' '} attribute :fi, 10 attribute :flag?, true end

And, in action, it would look like this:

>> f=Foo.new => # >> f.bar # defined, but not set to anything (nil) => nil >> f.fud # since bar is not defined, return an empty space => " " >> f.fi # just return the default => 10 >> f.flag? # and here's a boolean => true >> f.bar = 5 # now we set bar => 5 >> f.fud # Since bar is set, then fud will return its value => 5 >> f.fud = 20 # now we explicitly set fud, and the block is no longer used => 20 >> f.fud # fud returns 20 as expected => 20 >> f.bar # and, as expected, changing fud has no effect on bar => 5

There might be a better way to do this; but one of the things I love about Ruby is that you can add new features to the language very easily.

23Feb09 Overriding operators: two dimensional arrays

programming ruby

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: Image via Wikipedia

One of the neat things about ruby is that, in general, operators are methods, so they can be overridden.

When working with multidimensional arrays, some languages allow you to do the following:

a[0,0]

whereas ruby uses:

a[0][0]

Which makes sense, since Ruby implements it as an array of arrays and you’re chaining methods to get to the element. But, since we can override the [] method, we can then say a[0,0].

class Grid attr_reader :cols, :rows


  # initialize our grid and optionally prepopulate it.

  # klass can behave in the following fashions:

  # nil -- nil

  # a value (like "", 0, true) -- that value

  # a class which responds to new -- an instance of that class

   def initialize(rows=1, cols=1, klass = nil)

    @rows = rows

    @cols = cols

    @grid = (0 ... @rows).collect do |y|

      (0 ... @cols).collect do |x|

        if klass.nil? then

          nil

        elsif klass.respond_to? :new

          klass.new

        else

          klass

        end

      end

    end

  end
# This method allows us to say +grid[x, y]+ instead of +grid[y][x]+

  def [](x, y=nil)

    (x,y) = x if x.instance_of? Array

    @grid[y][x]

  end
  # This method allows us to set the value of a grid grid entry via

  # +grid[x, y]+ instead of +grid[y][x]+

  def []=(*args)

    if (args[0].instance_of? Array)

      ((x, y),value) = args

    else

      (x,y,value) = args

    end

    @grid[y][x] = value

  end

end

So, it can be used like this:

$ irb >> require 'grid' => true >> g=Grid.new => #< Grid:0xb747d760 @cols=1, @rows=1, @grid=[[nil]] > >> g=Grid.new(2,2) => #< Grid:0xb747bb04 @cols=2, @rows=2, @grid=[[nil, nil], [nil, nil]] > >> g=Grid.new(2,2,0) => #< Grid:0xb7479aac @cols=2, @rows=2, @grid=[[0, 0], [0, 0]] > >> g=Grid.new(2,2,String) => #< Grid:0xb7477810 @cols=2, @rows=2, @grid=[["", ""], ["", ""]] > >> g=Grid.new(2,2,false) => #< Grid:0xb74755d8 @cols=2, @rows=2, @grid=[[false, false], [false, false]] > >> g[0,0] => false >> g[0,0]=true => true >> g => #< Grid:0xb74755d8 @cols=2, @rows=2, @grid=[[true, false], [false, false]] >

It’s an interesting technique — and given that most people think of arrays/coordinates in pairs, I think that it can make the code more “readable”.

20Feb09 To Paren, or not to Paren

programming ruby

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To paren, or not to paren: that is the question:

Whether ’tis nobler in the mind to suffer

The bugs and errors of maintenance programs,

Or to take arms against a host of typos,

And by debugging end them? To hack: to slash;

No more; and by a slash to say we end

The heart-ache and the thousand natural shocks

Of cut and paste code, ’tis a maturation

Devoutly to be wished. To hack, not slash;

Not slash: perchance to code: ay, there’s the rub;

For in that new programme what code may come

When we have shuffled off this unix box,

Must give us pause: there’s the respect

That makes wuffy of so long life;

— Not William Shakespeare

There’s been a good deal of conversation of late on comp.lang.ruby as to whether or not to use parentheses. And when to use them. Ruby is such that parentheses are optional, except, of course, when they’re not. Here’s some examples of where they are not:

irb(main):002:0> "parenthesis".length() => 11 irb(main):003:0> "parenthesis".length => 11


...
irb(main):009:0> class Foo

irb(main):010:1> attr_accessor :bar, :groo

irb(main):011:1> attr_reader(:gruff)

irb(main):012:1> end

=> nil

irb(main):013:0> f=Foo.new

=> #

irb(main):014:0> f.gruff

=> nil

irb(main):015:0> f.bar

=> nil

Notice that Ruby also doesn’t care if you use parenthesis or not for the arguments; in this case it doesn’t matter whether or not the parenthesis are there, because the meaning is clear, at least to the compiler. And now, for something completely different, an instance where meaning is not clear to the compiler.

irb(main):016:0> class Foo irb(main):017:1> def fud(thing) irb(main):018:2> thing.reverse irb(main):019:2> end irb(main):020:1> end => nil irb(main):021:0> f.fud "hi" => "ih" irb(main):022:0> f.fud "hi" ? true : false (irb):22: warning: string literal in condition NoMethodError: undefined method `reverse' for true:TrueClass from (irb):18:in `fud' from (irb):22 from /usr2/jest/tools//lib/ruby/site_ruby/1.8/rubygems/dependency.rb:19 irb(main):023:0> f.fud("hi") ? true : false => true

In the first instance, it is trying to evaluate
"hi" ? true : false
and then pass it to f.fud. This doesn’t work very well, since true does not have a reverse method. We’re running into an issue of order of operation. However, when we do
f.fud("hi") ? true : false
then we are successful. “hi” can be reversed and the result can be checked for non-nil-ness. In this (admittedly simplistic) example, the parenthesis were needed in order to achieve a satisfactory result.

In terms of background, I learned C 20 years ago. I cut my teeth on basic back in 1980. So I’ve been around for a little while. I mention this because several posters mentioned that one’s preference for using parenthesis may depend on one’s background, with those who come from C potentially more likely to use parenthesis whether they were needed or not.

I am of the opinion that parenthesis can make the code harder to read.
attr_accessor :first, :last has_many :pets
is easier to my eyes and far easier to read as it mimics “natural” language than
attr_accessor(:first, :last) has_many(:pets)
However, I realize that it is a personal choice. So my rule of thumb is to not use parenthesis, except where there is a question of clarity. I think that writing clear, maintainable code is more important than adhering to a rule of always using parenthesis. I like that Ruby, like Unix, generally has more way than one to do a thing. I understand that there are people who prefer one way of doing a thing. For those people, there’s Python. I’m kidding, of course — you can adhere to doing things a single way, such as always using parenthesis, in Ruby. To me, however, it would lessen my enjoyment of the language. And I write code in Ruby because it makes me happy to do so.

So, what do you think? Is there a compelling reason to use parentheses?

19Feb09 my_methods revisited

programming ruby

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In irbrc goodness, I touched briefly on my_methods, a method of discovering the methods of an object which are distinct from those inherited from Object. The method looks like this:

class Object def my_methods (self.methods - Object.methods).sort end end
I have since had the idea of extending it — now you can also choose to see only the methods which are implemented by an object’s Class. You can see it in use here (code at the end):
$ irb
>> class Object
>> def my_methods(_super=false)
>> _methods = (_super) ? self.class.superclass.new.methods : Object.methods
>> (self.methods – _methods).sort
>> end
>> end
=> nil
>> class Foo < String >> def fud
>> puts “fud”
>> end
>> end
=> nil
>> f=Foo.new
=> “”
>> f.my_methods
=> [“%”, “*”, “+”, “<<", "[]", "[]=", "all?", "any?", "between?", "capitalize", "capitalize!", "casecmp", "center", "chomp", "chomp!", "chop", "chop!", "collect", "concat", "count", "crypt", "delete", "delete!", "detect", "downcase", "downcase!", "dump", "each", "each_byte", "each_line", "each_with_index", "empty?", "entries", "find", "find_all", "fud", "grep", "gsub", "gsub!", "hex", "index", "inject", "insert", "intern", "is_binary_data?", "is_complex_yaml?", "length", "ljust", "lstrip", "lstrip!", "map", "match", "max", "member?", "min", "next", "next!", "oct", "partition", "reject", "replace", "reverse", "reverse!", "rindex", "rjust", "rstrip", "rstrip!", "scan", "select", "size", "slice", "slice!", "sort", "sort_by", "split", "squeeze", "squeeze!", "strip", "strip!", "strip_tags", "sub", "sub!", "succ", "succ!", "sum", "swapcase", "swapcase!", "to_f", "to_i", "to_str", "to_sym", "tr", "tr!", "tr_s", "tr_s!", "unpack", "upcase", "upcase!", "upto", "zip"] >> f.my_methods(true)
=> [“fud”]
>>

Here’s the promised code:
class Object def my_methods(_super=false) _methods = (_super) ? self.class.superclass.new.methods : Object.methods (self.methods - _methods).sort end end

18Feb09 irbrc goodness

configuration programming ruby rubygems

2 Comments

Here’s my (current) .irbrc, with comments

# I am including gems in my irb session. Therefore, the next require require 'rubygems'


# wirble is a wonderful gem which add nice features to irb

require 'wirble'
# Dr. Nic's useful helper gem.  It makes it so you can say:

#   foo.map_by_bar

# instead of having to say:

#   foo.map{|f| f.bar}

# more to the point you can do

#   people.map_by_first_and_last

# instead of

#   people.map{|p| [p.first, p.last]}

require 'map_by_method'
# what_methods is a way to see which methods, when performed on an object, return a particular value:

# >> "hi".what? 'h'

# "hi".chop! == "h"

# "hi".chop == "h"

# => ["chop!", "chop"]

require 'what_methods'
# pretty print --> provides a "pretty" view of an object

require 'pp'
# auto indent irb; it's useful for when you're just experimenting

IRB.conf[:AUTO_INDENT]=true
# start wirble (with color)

Wirble.init

#Wirble.colorize
# What are the methods which belong only to an object, and not those inherited from Object

class Object

  def my_methods

    (self.methods - Object.methods).sort

  end

end

# strip html tags from a string class String def strip_tags self.gsub(/<\S[^><]*>/,"") end end

I’ve shown mine. Show me yours?

Here are links to the referenced rubygems:

16Feb09 Why ||=?

mini-saga programming ruby

0 Comments

||= is a very useful technique in Ruby programming and is used like:
x ||= 5
It relies on nil evaluating as false. It works like this: a variable is equal to its value xor some other value. If the variable is nil, then the other value is used. Otherwise, it keeps its value.

irb(main):001:0> x ||= 5 => 5 irb(main):002:0> x => 5 irb(main):003:0> y=2 => 2 irb(main):004:0> y ||= 7 => 2 irb(main):005:0> z NameError: undefined local variable or method `z' for main:Object from (irb):5 from :0 irb(main):006:0> z=nil => nil irb(main):007:0> z ||= 3 => 3 irb(main):008:0> m NameError: undefined local variable or method `m' for main:Object from (irb):8 from :0 irb(main):009:0> m ||= 1 => 1 irb(main):010:0>

15Feb09 It went (that) way

mini-saga programming ruby

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: Image via Wikipedia

Ruby supports operator overloading — operators behave as methods of an object. So, << behaves differently based on the context. Generally for anything other than bit shifting << means to append or concatenate, such as with a string or an array. Concatenate is generally faster than addition — new objects are not created.

matt:~$ irb >> 32 << 3 => 256 >> "cat" << 'nip' => "catnip" >> [0,2] << 2 => [0, 2, 2]

14Feb09 Open-uri makes for developer friendly I/O

mini-saga programming ruby

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: Image via Wikipedia

open-uri, a part of the standard Ruby distribution, makes opening and reading from a URI easy. With it, developers use familiar methods like open for performing I/O with URI’s.

require 'open-uri' open("http://www.ruby-lang.org/") {|f| f.each_line {|line| p line} }

Contrast Net::HTTP which uses numerous methods to achieve the same effect.

require 'net/http'

url = URI.parse('http://www.example.com/index.html') req = Net::HTTP::Get.new(url.path) res = Net::HTTP.start(url.host, url.port) {|http| http.request(req) } puts res.body

An addon, SuperIO, adds more flexiblity in attempting to DTRT.

13Feb09 Holy Ruby Methods, Batman!

mini-saga programming ruby

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bang! Conventions are one of Ruby‘s nicest features, making it easier to read and maintain. One convention is that methods which may modify an object have a ‘!’ in their name, such as ‘chop!’, which indicates if there are no changes, then nil is returned. This can cause issues with method chaining.

13Feb09 Recursion

programming ruby

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A question was raised on comp.lang.ruby by Li Chen regarding recursion being used to convert decimals to binary. What follows is my response.
Continue reading ‘Recursion’

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