symbol

change string to symbol:

use to_sym or intern

ex:

"test".to_sym

--->  :test

change symbol to string

method 1: use to_s

method 2: use #{ }

ex:

"#{:abc}"

---> "abc"

methods

methods:

A.methods:

show class methods

A.methods(false):

only show class methods of A, not including inherited methods

a.methods:

show instance methods of a

instance_methods:

A.instance_methods equals a.methods

A.instance_methods(false):

show only instance_methods 0f A, not including inherited methods

private_methods, public_methods, protected_methods, singleton_methods

compare: equal?, Comparable module

check  whether  two objects are the same object

define how to compare

use Comparable module & define <=> method

the return value of method <=> ,  1, 0 , & -1 decides greater than, equal than, & less than

ex:

class Rabbit

     include Comparable 

     attr_accessor  :name

     def  <=> (other_rabbit)

          if  self.name <>

                  -1

          elsif  self.name > other_rabbit.name

                  1

          else

                  0

          end 

     end

end

if the thing to compare know how to compare, there is a shorter definition

ex:

def  <=> (other_rabbit)

       self.name<=> other_rabbit.name

end

true, false & nil

In Ruby, nil & false  are the only two objects have boolean value of false

for, each

for

ex:

for a in [1,2,3]

puts a

end

each

ex:

[1,2,3].each do |i|

puts i

end

loop, while, until

loop

ex:

loop do

    a=a+1

    break if a>3

end

loop do 

     a=a+1

     next if a <3

     break

end

while

ex:

while a<3

end

until:

ex:

until a>3

end

case

ex:

case  name

when "peter"

puts "peter"

when "andy"

puts  "andy"

else

puts  "others"

end

how it works

translate to 

if "peter" === name

note: the === method can be customarily defined