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Ruby language is dynamic and robust. We can define methods inside ruby classes at runtime.
# bash class A define_method :a do puts "hello" end define_method :greeting do |message| puts message end end A.new.a #=> hello A.new.greeting 'Ram ram' #=> Ram ram
Can you imagine using dynamic methods below 24 lines of code is optimized to just 8 lines
To know more on below code read # Earlier code class ApplicationController < ActionController::Base protect_from_forgery helper_method :current_staff, :current_employee, current_admin def authenticate_staff!(opts={}) current_staff || not_authorized end def current_staff current_user if current_user.is_a? Staff end def authenticate_employee!(opts={}) current_employee || not_authorized end def current_employee current_user if current_user.is_a? Employee end def authenticate_admin!(opts={}) current_admin || not_authorized end def current_admin current_user if current_user.is_a? Admin end end
# New Version using dynamic methods %w(Staff Employee Admin).each do |k| define_method "current_#{k.underscore}" do current_user if current_user.is_a?(k.constantize) end define_method "authenticate_#{k.underscore}!" do |opts={}| send("current_#{k.underscore}") || not_authorized end end

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Alias method in ruby
Ruby classes provides a alias_method that can be used to reuse the existing methods.
Consider a situation where you need different methods which has same code and ONLY they have different names.

In this case alias_method uses suits best choice instead duplicating same code or writing common method that will get used in all methods, as i did before. Example, I have methods search, home, index all are doing same functionality.
Old approach # URL / def index list end # URL /search def search list end #URL /home def home list end private def list # code here end Correct approach in ruby def index # code here end alias_method :home, :index alias_method :search, :index Attributes aliasing in ruby
Same way one can easily rename existing class attribute names using alias_attribute method.
alias_attribute(new_name, old_name) alias_attrinute :username, :login More practical use
while deprecating attributes, methods in gems, plugins, extensions, libraries always use aliases in order to maintain backward compatibility.
Got easy ??
that's where ruby rocks !

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Eval method in ruby executes string/expression passed as parameter.
Example:
irb > eval("5+3") => 8 irb > eval("a=5") => 5 irb > eval("b||=a") => 5
Its part of ruby meta-programming and not recommended approach unless there is no any alternative to do.