Ruby Object Types and Control Structures

Ruby Object Types

Variables

• Everything is ruby is an object execpt variables.
• ruby variable convention: all lowercase underscore
• 大写开头或全大写会被认为是 constant

Variable Scope and Indicators

String

• ruby 单引号相当于 python 的 repr（verbatim 一字不差）
• 变量替换 #{var_name} 括号内可求值
• %Q{string} treat this string the same as if it had been in double quotes
• %q{string} treat this string the same as if it had been in single quotes

Arrays

• array[index] 如果这个位置没有obj，返回nil而不是报错
• array[index] = obj，如果index没有值，中间用nil填补
• array « value，append obj到array，性能最佳
• array.push(obj) 同上
• array.pop 删除并返回最后一个element
• array.shift 删除并返回第一个element
• array.unshift(obj) 把obj添加到最头上
• array.delete_at(index)，返回被删除的obj，如果index无，返回nil
• array.delete(obj)，删除array中的某个obj，如无，返回nil
• inspect 返回string
• array可以加减，但是不改变array本身。如果减自身没有的，则返回自身

Arrays operation

Union operator

union_example = ["a", "b", "a"] | ["c", "c"]
p union_example
=> ["a", "b", "c"]

Intersection operator

>> intersection = ['a', 'b', 'c'] & ['b', 'c']
=> ["b", "c"]

Difference operator

>> array_difference = [1,2,3, 1,2,3] - [1]
=> [2, 3, 2, 3]

hash

创建新hash

# 常用方法
options = { :font_size => 10, :font_family => "Arial" }
options = { font_size: 10, font_family: "Arial" }

# 特别方法一
>> chuck_norris = Hash[:punch, 99, :kick, 98, :stops_bullets_with_hands, true]
=> {:punch=>99, :kick=>98, :stops_bullets_with_hands=>true}
>> chuck_norris
=> {:punch=>99, :kick=>98, :stops_bullets_with_hands=>true}
# 特别方法二
>> a = [:a, 1]
=> [:a, 1]
>> b = [:b, 2]
=> [:b, 2]
>> c = [a, b]
=> [[:a, 1], [:b, 2]]
>> d = Hash[c]
=> {:a=>1, :b=>2}
>> d
=> {:a=>1, :b=>2}

# 用class.new method可以设置初始值
>> h = Hash.new('default')
=> {}
>> h[:anything]
=> "default"

hash.key(value)，返回这个value的key；如无，返回nil

symbol

feature

• A label used to identify a piece of data
• A symbol is only stored in memory one time, string created many times.
• like an immutable string whose value is itself
• symbols are not variables

>> nil.respond_to?(:to_i)
=> true
>> :to_i
=> :to_i
>> nil.to_i
=> 0

>> "test".object_id
=> 70346480937300
>> "test".object_id
=> 70346480906760
>> :test.object_id
=> 355868
>> :test.object_id
=> 355868

usage

• use symbol as keys in hashes to avoid the same key in different hashes
• use symbol to pass messages around between different parts of program

range

• range在ruby里是Range Class的instance，不是array
• Exclusive range 1…10 (like python range)
• Inclusive range 1..10
• 他们的end或者last都返回10
• [*range] 可以把range展开成array
• 'a'..'m' 也是range

Constants

• Constants are similar to variables
  • Not true objects
  • point to objects
• Constants are different than variables
  • A contant is constant
• 大写开头都会被认为是constant
• 改变Constant的pointer会被警告

Boolean

• true.class :=> TrueClass
• false.class :=> FalseClass
• ALL values in Ruby are evaluated to true, EXCEPT for FALSE and NIL.

>> if 0
>>   puts "Hey, 0 is considered to be a truth in Ruby"
>> end
Hey, 0 is considered to be a truth in Ruby
=> nil

Control Structures

unless

与if相反, unless 是ruby中对false的检测。如果unless后面跟false，则执行它的从句，通常用于检测x有没有。

>> puts "Yes!" if true
Yes!
=> nil
>> puts "No!" unless false
No!
=> nil
>> puts "No!" unless true
=> nil

换行时要注意

raise("Boom!") unless
  ship_stable # 可以正确parsing
  
raise("Boom!") 
  unless (ship_stable) # 报错，因为上一个句子本身是一个statement

case

case test_value
when value
  ...
when value
  ...
else
  ...
end

ternary operator

boolean ? code1 : code2

or

x = y || z
# means
if y
  x = y
else
  x = z
end

or-equals

x ||= y
# means
x = y unless x

LOOPS

Loop control keywords

• break = Terminiate the whole loop
• next = Jump to the next loop
• redo = Redo this loop
• retry = Start the whole loop over

Examples:

>> x = 0
=> 0
>> puts x += 2 while x < 10
2
4
6
8
10
=> nil

>> y = 3245
=> 3245
>> puts y /= 2 until y <= 1
1622
811
405
202
101
50
25
12
6
3
1
=> nil

iterators

• Integer/floats: times, upto, downto, step
• Range: each, step
• String: each, each_line, each_byte
• Array: each, each_index, each_with_index
• Hash: each, each_key, each_value, each_pair

Examples:

5.times do
  puts "Hello"
end

1.upto(5) {puts "Hello"}
5.downto(1) {puts "Hello"}
(1..5).each {puts "Hello"}

>> 1.upto(5) do |i|
?>   puts "hello" + i.to_s
>> end
hello1
hello2
hello3
hello4
hello5
=> 1

>> fruits = ['banana', 'apple', 'pear']
=> ["banana", "apple", "pear"]
>> fruits.each do |fruit|
?>   puts fruit.capitalize
>> end
Banana
Apple
Pear
=> ["banana", "apple", "pear"]

>> for fruit in fruits
>>   puts fruit.capitalize
>> end
Banana
Apple
Pear
=> ["banana", "apple", "pear"]