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Keith Bennett : What I Love About Ruby

This page last changed on Sep 17, 2008 by kbennett.

What I Love About Ruby
Keith Bennett

kbennett .at. bbsinc .dot. biz

Simplicity of Creating Instance Variables with Accessors and Mutators in Ruby

class Y
attr_accessor :a
end

...creates an instance variable a, and an accessor and mutator.

Concise Idiom for Conditional (and Lazy) Initialization

@var ||= some_expensive_initialization

...means if var is undefined, define it, and if nil, do the initialization.

Numeric Constants Thousands Separators Supported

irb(main):002:0> 1_000_000
=> 1000000
irb(main):003:0> 1_000_000.class
=> Fixnum

Actually, all underscores are stripped, even if they do not separate thousands.

Shell Integration

A shell command enclosed in backticks will be run, and the value returned by the backticked command
will be the text the command sent to stdout:

irb(main):008:0> `mkdir a b c d`
=> ""
irb(main):009:0> `touch b/foo d/foo`
=> ""
irb(main):010:0> emptydirs = `find . -type d -empty`
=> "./an./cn"
irb(main):011:0> puts emptydirs
./a
./c
=> nil

Logical Syntax:

1.upto(10) { |i| puts i }

(100..200).each { |n| puts n }

Document generated by Confluence on Sep 18, 2008 09:45 Page 1

vs., in Java, for the first example:

for (int i = 0; i <= 10; i++) {
System.out.println(i) ;
}

Ability to Specify Arrays (and Hashes) as Literals

and the Ease of Iterating Over Them

irb(main):018:0> ['collie', 'labrador', 'husky'].each { |breed|
puts "Hi, I'm a #{breed}, and I know how to bark."
}
Hi, I'm a collie, and I know how to bark.
Hi, I'm a labrador, and I know how to bark.
Hi, I'm a husky, and I know how to bark.
=> ["collie", "labrador", "husky"]

Also:

%w(collie labrador husky)

can be used to create the array instead of:

['collie', 'labrador', 'husky']

A Hash:

irb(main):063:0> favorites = { :fruit => :durian, :vegetable => :broccoli }
=> {:fruit=>:durian, :vegetable=>:broccoli}

Ranges

water_liquid_range = 32.guatda.com/cmx.p0...212.0
=> 32.guatda.com/cmx.p0...212.0
irb(main):010:0> water_liquid_range.include? 40
=> true
irb(main):011:0> water_liquid_range.include? -40
=> false

Note: Ranges are not arrays; any number n, not just integers, such that 32.0 <= n < 212.0, is included
in the range.

Converting Ranges to Arrays:

irb(main):043:0> ('m'..'q').to_a
=> ["m", "n", "o", "p", "q"]

Blocks Used to Automatically Close Resources

File.open 'x.txt', 'w' do |file|
file << 'Hello, world'


end

The file is automatically closed after the block completes. If no block is provided, then the open function
returns the file instance:

irb(main):001:0> f = File.open 'x.txt', 'w'
=> #<File:x.txt>
irb(main):002:0> f << "Pleaaase, delete me, let me go..."
=> #<File:x.txt>
irb(main):003:0> f.close
=> nil
irb(main):004:0> puts IO.read('x.txt')
Pleaaase, delete me, let me go...
=> nil

Simple File Operations

file_as_lines_array = IO.readlines 'x.txt'
file_as_single_string = IO.read 'x.txt'

Clean and Simple Syntax

puts Array.instance_methods.sort

Regular Expressions

irb(main):027:0> 'ruby' =~ /ruby/
=> 0
irb(main):028:0> 'rubx' =~ /ruby/
=> nil
irb(main):029:0> 'ruby' =~ /Ruby/
=> nil
irb(main):030:0> 'ruby' =~ /Ruby/i
=> 0

Arrays:

irb(main):001:0> nums = [1,2,3,4,5]
=> [1, 2, 3, 4, 5]
irb(main):006:0> nums.include? 3
=> true
irb(main):004:0> nums.collect { |n| n * n }
=> [1, 4, 9, 16, 25]
irb(main):002:0> nums.reject { |n| n % 2 == 0}
=> [1, 3, 5]
irb(main):003:0> nums.inject { |sum,n| sum += n }
=> 15
irb(main):052:0* distances_in_miles = [10, 50]=> [10, 50]
irb(main):053:0> distances_in_km = distances_in_miles.map { |n| n * 9.0 / 5.0 }
=> [18.0, 90.0]irb(main):016:0* twos = (0..10).map { |n| n * 2 }
=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
irb(main):017:0> fours = (0..5).map { |n| n * 4 }
=> [0, 4, 8, 12, 16, 20]
irb(main):018:0> twos - fours
=> [2, 6, 10, 14, 18]
irb(main):019:0> twos & fours


=> [0, 4, 8, 12, 16, 20]
irb(main):020:0> fours * 2
=> [0, 4, 8, 12, 16, 20, 0, 4, 8, 12, 16, 20]
irb(main):021:0> twos + fours
=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 0, 4, 8, 12, 16, 20]

Built-in String Operations

• Case Conversions, Capitalization
• Left, Right, Sub
• Strip, Justify, Center
• Search and Replace (gsub)
• Insert, Delete


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