Ruby01: Beginner

中整個早上都忙著作業，看來是假期懶了一下現在現眼報吧哈哈。在上課之前發一下Ruby 的首章，算是倉促的開始吧。

puts

puts "Once upon a time...

there's a self learn programmer...."　　 #okay

puts

"Once upon a time...

there's a self learn programmer...."　　# output: *blank*

所以Ruby 是case-sensitive 咯？但在網上卻是這樣說：“Whitespace characters such as spaces and tabs are generally ignored in Ruby code, except when they appear in strings. ”(Tutorial Point)。所以，我們推斷 Ruby command 是不可以被分開的。

puts vs print

puts "Hello World"　　#auto-append "\n"

print "I am in "　　　　#not appending "\n"

print "campus"

output:

Hello World

I am in campus

啊，要去上課了，待續...

https://www.tutorialspoint.com/ruby/ruby_comments.htm

BEGIN{} & END{} Priorities

puts "in the middle, even written in front?! "

BEGIN{
puts "prog initialize"
}

END{
puts "just before prog termination"
}

output:

prog initialize

in the middle, even written in front?!

just before prog termination

Block commenting

=begin
block comment
instead of using #
=end

Class in Ruby

#in Ruby, everything treated as object

 #in Ruby, everything treated as object 

 $ monthly_customers = 0; 

 class Customer
     @@no_of_customers = 0;         #class var: static DM: all obj share 1 copy

     #member function in ruby class
     def initialize(id, name, addr)    #initialize: the reserved method for constructors
 #lowercase letters for method name
     @cust_id = id    #instance var == DM
     @cust_name = name
     @cust_addr = addr
     end 

     def modify_addr(addr2)
     ::Customer.instance_variable_get(:@cust_addr) = addr2    #modify instance var in same class
     end 

 end

 cust1 = Customer.new(", "Amy", "CauswayBay, HK")
 cust2 = Customer.new;
 p cust2.instance_variable_get(:@cust_id)    #nil: access uninitialized instance variable
 cust2.initialize(", "Timonthy", "Kwai Shing")
 p cust2.instance_variable_get(:@cust_id)    # "02"

差不多要上課了，待續...

https://www.tutorialspoint.com/ruby/ruby_variables.htm
https://www.tutorialspoint.com/ruby/ruby_class_case_study.htm

Global variable in Ruby

$global_variable = "Hello kitty"  #define a global var
class Class1
  def print
    puts "Global variable is: #$global_variable"    #access global var
  end
end   #to finish class definition

class1obj = Class1.new
class1obj.print   #no global fnc in ruby: fnc involved by obj only

Local variable, constant & execution order

$global_variable = "Hello kitty"  #define a global var
class Class1
  @@object_Counter = 1    #no space btw '@@' and identifier name
  FIXED_VALUE = 100     #const var starts with capital, local var starts with lower case 

  def print
    @local_var = "Hello global"
    puts "Global variable is: #$global_variable"    #access global var
    puts "Instance varable ~ DM: #@local_var"     #access instance var
    puts "Existing objects = #@@object_Counter"
  end

  puts "when local variable out of scope: #@local_var"
  # codes defined out of any class method executed first: ~ global MF

  puts "The constant in class : #{FIXED_VALUE}"     #access constant  

end   #to finish class definition

class1obj = Class1.new
class1obj.print   #no global fnc in ruby: fnc involved by obj only

output:

when local variable out of scope:
The constant in class : 100
Global variable is: Hello kitty
Instance varable ~ DM: Hello global
Existing objects = 1
=> nil

to be continued...