Installing Scheme 9.2 on Mac OS 10.10.5

1. Download 64-bit installer mit-scheme-9.2-x86-64.dmg
2. Install Scheme.
3. sudo ln -s /Applications/MIT\:GNU\ Scheme.app/Contents/Resources /usr/local/lib/mit-scheme-x86-64
4. sudo ln -s /usr/local/lib/mit-scheme-x86-64/mit-scheme /usr/local/bin/scheme
5. Type scheme on the terminal.

undefined method `want=' for nil:NilClass (NoMethodError)

In Rails 4.2, you can define your own application specific custom variables in development.rb, test.rb and so on. If you define this:

  config.x.whatever.value.want = 42

It throws the error : undefined method `want=' for nil:NilClass (NoMethodError)

It seems to work only for two levels, so, this will work:

  config.x.whatever.value = 42

You can access the value like this:

Rails.configuration.x.whatever.value

You need to define the custom values by using 'config.x'.

Error in The Well Grounded Rubyist Book

David Black says "The only circumstances under which you can omit the receiver are precisely the circumstance in which it's ok to call a private method."

 This is not true because we can omit the receiver when we call the class method declared in the superclass. ActiveRecord has_many declaration is an example.

Looking for Ruby Book Reviewers

I am looking for technical reviewers to review Essential Ruby Kindle book. I will mention your name and give a link to your site or blog  in the book. If you are interested, please contact me at bparanj at gmail dot com or RubyPlus contact form.

Abstraction Diagrams

How to find out if a name is reserved in Rails 4.2.5

One of the articles that gets lot of traffic is : Reserved Words in Rails. If you do not use the generator to generate the code in your Rails project, you could potentially have class collision during runtime of your application. Here are the steps I followed:

1. I browsed the railties gem and searched for 'reserved by Ruby on Rails' to find where in the source code the check is done.
2. It is defined in the class rails/generators/base.rb in class_collisions(*class_names) protected method.
3. I went to the rails console to figure out how to use this method:

> require 'rails/generators/base'
NameError: uninitialized constant Rails::Generators::Actions
from /Users/bparanj/.rvm/gems/railties-4.2.5/lib/rails/generators/base.rb:17:in `'
pry(main)> require 'rails/generators/actions'
=> true
 pry(main)> require 'rails/generators/base'
=> true
 pry(main)> g = Rails::Generators::Base.new
=> # @_initializer=[[], {}, {}],
 @_invocations={},
 @after_bundle_callbacks=[],
 @args=[],
 @behavior=:invoke,
 @destination_stack=["/Volumes/Work/dev/ewok"],
 @in_group=nil,
 @options={},
 @shell=#, @mute=false, @padding=0>>
 pry(main)> g.send(:class_collisions, 'ActiveRecord')
Rails::Generators::Error: The name 'ActiveRecord' is either already used in your application or reserved by Ruby on Rails. Please choose an alternative and run this generator again.
pry(main)> g.send(:class_collisions, 'type')
=> ["type"]
pry(main)> g.send(:class_collisions, 'ActiveRecord', 'ActiveJob')
Rails::Generators::Error: The name 'ActiveRecord' is either already used in your application or reserved by Ruby on Rails. Please choose an alternative and run this generator again.

Methods Live in Class

$ irb
2.2.4 :001 > s = 'hi'
 => "hi"
2.2.4 :002 > s.methods
 => [:<=>, :==, :===, :eql?, :hash, :casecmp, :+, :*, :%, :[], :[]=, :insert, :length, :size, :bytesize, :empty?, :=~, :match, :succ, :succ!, :next, :next!, :upto, :index, :rindex, :replace, :clear, :chr, :getbyte, :setbyte, :byteslice, :scrub, :scrub!, :freeze, :to_i, :to_f, :to_s, :to_str, :inspect, :dump, :upcase, :downcase, :capitalize, :swapcase, :upcase!, :downcase!, :capitalize!, :swapcase!, :hex, :oct, :split, :lines, :bytes, :chars, :codepoints, :reverse, :reverse!, :concat, :<<, :prepend, :crypt, :intern, :to_sym, :ord, :include?, :start_with?, :end_with?, :scan, :ljust, :rjust, :center, :sub, :gsub, :chop, :chomp, :strip, :lstrip, :rstrip, :sub!, :gsub!, :chop!, :chomp!, :strip!, :lstrip!, :rstrip!, :tr, :tr_s, :delete, :squeeze, :count, :tr!, :tr_s!, :delete!, :squeeze!, :each_line, :each_byte, :each_char, :each_codepoint, :sum, :slice, :slice!, :partition, :rpartition, :encoding, :force_encoding, :b, :valid_encoding?, :ascii_only?, :unpack, :encode, :encode!, :to_r, :to_c, :unicode_normalize, :unicode_normalize!, :unicode_normalized?, :>, :>=, :<, :<=, :between?, :nil?, :!~, :class, :singleton_class, :clone, :dup, :itself, :taint, :tainted?, :untaint, :untrust, :untrusted?, :trust, :frozen?, :methods, :singleton_methods, :protected_methods, :private_methods, :public_methods, :instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :instance_of?, :kind_of?, :is_a?, :tap, :send, :public_send, :respond_to?, :extend, :display, :method, :public_method, :singleton_method, :define_singleton_method, :object_id, :to_enum, :enum_for, :equal?, :!, :!=, :instance_eval, :instance_exec, :__send__, :__id__]
2.2.4 :003 > s.instance_methods
NoMethodError: undefined method `instance_methods' for "hi":String
    from (irb):3
    from /Users/bparanj/.rvm/rubies/ruby-2.2.4/bin/irb:11:in `

'
2.2.4 :004 > String.instance_methods
 => [:<=>, :==, :===, :eql?, :hash, :casecmp, :+, :*, :%, :[], :[]=, :insert, :length, :size, :bytesize, :empty?, :=~, :match, :succ, :succ!, :next, :next!, :upto, :index, :rindex, :replace, :clear, :chr, :getbyte, :setbyte, :byteslice, :scrub, :scrub!, :freeze, :to_i, :to_f, :to_s, :to_str, :inspect, :dump, :upcase, :downcase, :capitalize, :swapcase, :upcase!, :downcase!, :capitalize!, :swapcase!, :hex, :oct, :split, :lines, :bytes, :chars, :codepoints, :reverse, :reverse!, :concat, :<<, :prepend, :crypt, :intern, :to_sym, :ord, :include?, :start_with?, :end_with?, :scan, :ljust, :rjust, :center, :sub, :gsub, :chop, :chomp, :strip, :lstrip, :rstrip, :sub!, :gsub!, :chop!, :chomp!, :strip!, :lstrip!, :rstrip!, :tr, :tr_s, :delete, :squeeze, :count, :tr!, :tr_s!, :delete!, :squeeze!, :each_line, :each_byte, :each_char, :each_codepoint, :sum, :slice, :slice!, :partition, :rpartition, :encoding, :force_encoding, :b, :valid_encoding?, :ascii_only?, :unpack, :encode, :encode!, :to_r, :to_c, :unicode_normalize, :unicode_normalize!, :unicode_normalized?, :>, :>=, :<, :<=, :between?, :nil?, :!~, :class, :singleton_class, :clone, :dup, :itself, :taint, :tainted?, :untaint, :untrust, :untrusted?, :trust, :frozen?, :methods, :singleton_methods, :protected_methods, :private_methods, :public_methods, :instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :instance_of?, :kind_of?, :is_a?, :tap, :send, :public_send, :respond_to?, :extend, :display, :method, :public_method, :singleton_method, :define_singleton_method, :object_id, :to_enum, :enum_for, :equal?, :!, :!=, :instance_eval, :instance_exec, :__send__, :__id__]

Changing Self inside the Block

(1..10).tap {|x| puts "original: #{x.inspect}"}.tap {|x| puts "Original class: #{x.class}"}.to_a.tap {|x| puts "array: #{x.inspect}"}.tap {|x| puts "After class: #{x.class}"}

gzip http header

Color Blind Test