Ruby 知识点速查

$ gem install bundler -v 1.17
$ gem install minitest -v 5.8.4

# 使用 Bundler 更新单个 gem
$ bundle update nokogiri
# 使用 Bundler 更新 Gemfile 中的每个 gem
$ bundle update

# 单行注释
=begin
多行
注释
=end
=begin 注释第 1 行 =end
puts "Hello world!"  # 代码的内联注释

current_weather = "rainy"
_weather = "sunny"

必须以下划线或小写字母开头

# 实例类变量
@current_weather = "rainy"
# 全局变量
$current_weather = "rainy"
# 常量变量
WEATHER = "rainy".freeze

defined? count
"local-variable"
defined? @id
"instance-variable"
defined? @@name
"class variable"
defined? $version
"global-variable"
defined? PI
"constant"

# 两者都是同义词
a = 37
a.kind_of? Integer
# true
a.is_a? Integer
# true

week_days = {sunday: 11, monday: 222}

2.even?
# true
3.even?
# false

.. 用于创建包含范围

range = 1..10
range.to_a
# 输出 => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

... 用于创建专属范围

range = 1...10
range.to_a
# 输出 => [1, 2, 3, 4, 5, 6, 7, 8, 9]

一些有用的方法

(1..20).step(2) { |number| puts "#{number}"}
# 输出
# 1
# 3
# 5
# 7
# 9
# 11
# 13
# 15
# 17
# 19

num = 2
puts 'two' if num == 2 

如果条件为真，则执行代码

temp = 19
if temp >= 25
  puts "hot"
elsif temp < 25 && temp >= 18
  puts "normal"
else
  puts "cold"
end
# 输出 => normal

# 除非与 if 相反，当语句为假时进行评估
name = "rob"
# if name != "bob"
unless name == "bob"
  puts "hello stranger"
else
  puts "hello bob"
end
# 输出 => hello stranger
num = 6
puts 'not two' unless num == 2
# 输出 => not two

case input
  when 19 then puts "It's 19"
end

case input
  when 19 then puts "It's 19"
else
  puts "It's not 19"
end

marks = 86
result = case marks
        when 0..49 then "Fail"
        when 50..64 then "Pass"
        when 65..74 then "Credit"
        when 75..84 then "Distinction"
        when 85..100 then "High Distinction"
        else "Invalid marks"
        end

puts result
# High Distinction

name = "World"
puts "Hello #{name}"
puts "The total is #{1+1}"
# "the total is 2"

字符串插值允许您将字符串组合在一起

string = "abc123"
string[0,3]
# "abc"
string[3,3]
# "123"
string[0..-2]
# "abc12"
#remove or replace the substring
string[0..2] = ""
puts string
# "123"

子字符串是字符串的一小部分，如果你只想要那个特定的部分，它会很有用，比如开头、中间或结尾

"HELLO World".downcase  # "hello world"
"hello worlD".upcase    # "HELLO WORLD"
"hEllo wOrlD".capitalize # "Hello world"
"hEllo WOrlD".swapcase  # "HeLLO woRLd"

res = method_name(parameter1, parameter2)
# 可以调用不带括号的方法
res = method_name parameter1, parameter2

def method_name(num1, num2 = num1)
    return num1 + num2
end
res = method_name(10)
# 输出 => 20

def method_name(parameter1, parameter2, type = "ADD")
    puts "#{parameter1} #{parameter2}"
    return parameter1 + parameter2 if type == "ADD"
    return parameter1 - parameter2 if type == "SUB"
end
res = method_name(20, 10)
# 输出 => 30

def method_name(type, *values)
    return values.reduce(:+) if type == "ADD"
    return values.reduce(:-) if type == "SUB"
end
numbers = [2, 2, 2, 3, 3, 3]
res = method_name("ADD", *numbers)
# 输出 => 15
res = method_name("SUB", *numbers)
# 输出 => -11
# 或者您可以提供这样的值
res = method_name("ADD", 2, 2, 2, 3, 3, 3)
# 输出 => 15

a = ["Drama", "Mystery", "Crime",
"Sci-fi", "Disaster", "Thriller"]
a.sort
puts a
# 我们没有修改对象
# Drama
# Mystery
# Crime
# Sci-fi
# Disaster
# Thriller
a.sort!
puts a
# 修改对象
# Crime
# Disaster
# Drama
# Mystery
# Sci-fi
# Thriller

当您要修改对象时，在方法之后使用 !

在 ruby 中，以问号 (?) 结尾的方法称为布尔方法，它返回 true 或 false

"some text".nil?
# false
nil.nil?
# true

您可以拥有自己的布尔方法

def is_vowel?(char)
    ['a','e','i','o','u'].include? char
end
is_vowel? 'a'
# true
is_vowel? 'b'
# false

# return value
def give_me_data
    data = yield
    puts "data = #{data}"
end
give_me_data { "Big data" }
# 输出 => data = Big data

do 和 end（用于多行）或花括号 { 和 }（用于单行）之间的代码称为块，它们可以在两个管道之间定义多个参数 (|arg1, arg2|)

salary = [399, 234, 566, 533, 233]
salary.each { |s| puts s }
# puts s = block body
# |s| = block arugments

salary.each do |s|
    a = 10
    res = a * s
    puts res
end
# 块体
# a = 10
# res = a * s
# puts res
# 块参数
# |s|

块可以作为方法参数传递，也可以与方法调用相关联。 块返回最后评估的语句

def give_me_data
    puts "I am inside give_me_data method"
    yield
    puts "I am back in give_me_data method"
end

give_me_data { puts "Big data" }

# 输出
# I am inside give_me_data method
# Big data
# I am back in give_me_data method

def give_me_data
    yield
    yield
    yield
end

give_me_data { puts "Big data" }

# 输出
# Big data
# Big data
# Big data

def give_me_data
    yield 10
    yield 100
    yield 30
end

give_me_data { |data| puts "Big data #{data} TB" }

# 输出
# Big data 10 TB
# Big data 100 TB
# Big data 30 TB

def give_me_data
    yield "Big data", 10, "TB"
    yield "Big data", 100, "GB"
    yield "Big data", 30, "MB"
end

give_me_data { |text, data, unit| puts "#{text} #{data} #{unit}" }

# 输出
# Big data 10 TB
# Big data 100 GB
# Big data 30 MB

give_me_data
    puts "我在 give_me_data 方法里面"
end

def test
  puts "我在测试方法里面"
  give_me_data { return 10 } # 代码从这里返回
  puts "I am back in test method"
end

return_value = test

# 输出
# 我在测试方法里面
# 我在 give_me_data 方法里面
# 10

def give_me_data(&block)
    block.call
    block.call
end

give_me_data { puts "Big data" }

# 输出
# Big data
# Big data

def give_me_data
    yield
end

give_me_data

# 输出
# LocalJumpError: no block given (yield)

def give_me_data
    return "no block" unless block_given?
    yield
end

give_me_data { puts "Big data" }
give_me_data

# 输出
# Big data

p = Proc.new { return 10 }
p.call
# 输出
LocalJumpError: unexpected return

def give_me_data
    puts "我在 give_me_data 方法里面"
    p = Proc.new { return 10 }
    p.call # 代码从这里返回
    puts "I am back in give_me_data method"
end

return_value = give_me_data
puts return_value

# 输出
# 我在 give_me_data 方法里面
# 10

l = -> (count) { "Hello World " * count }
l.call 5
# 输出
# "Hello World Hello World Hello World Hello World Hello World "
l.call 5, 2
# 输出
wrong number of arguments (given 2, expected 1)

l = -> { return 10 }
l.call

# 输出 => 10

array = Array.new   #=> []
# or
array = []

array = [1, "two", 3.0] 
#=> [1, "two", 3.0]

temperature_data = [
              ["A908", 38],
              ["A909", 37],
              ["A910", 38],
          ]
temperature_data[0]    #=> ["A908", 38]
temperature_data[0][0] #=> "A908"
temperature_data[0][1] #=> 38

str_array = [
  "This", "is", "a", "small", "array"
]
str_array[0]            #=> "This"
str_array[1]            #=> "is"
str_array[4]            #=> "array"

str_array = [
  "This", "is", "a", "small", "array"
]
# 索引 -1 表示最后一个元素
str_array[-1]        #=> "array"
# 索引 -2 表示倒数第二个元素
str_array[-2]        #=> "small"
str_array[-6]        #=> nil

str_array = [
  "This", "is", "a", "small", "array"
]

puts str_array.at(0)      #=> "This"

arr = [1, 2, 3, 4, 5, 6]
arr[100]                  #=> nil
arr[-3]                   #=> 4
arr[2, 3]                 #=> [3, 4, 5]
arr[1..4]                 #=> [2, 3, 4, 5]
arr[1..-3]                #=> [2, 3, 4]

arr = ['a', 'b', 'c', 'd', 'e', 'f']
arr.fetch(100)
#=> IndexError: 数组边界外的索引 100：-6...6
arr.fetch(100, "oops")    #=> "oops"

超出边界，给默认值

arr = [1, 2, 3, 4, 5, 6]

arr.first     # 第一个值 => 1
arr.last      # 最后一个值 => 6
# take 返回前 n 个元素
arr.take(3)   #=> [1, 2, 3]
# drop 在 n 个元素被删除之后
arr.drop(3)   #=> [4, 5, 6]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.push(11)          
#=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
numbers.push(12, 13, 14)  
#=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

num_array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
num_array.pop             #=> 10
num_array
#=> [1, 2, 3, 4, 5, 6, 7, 8, 9]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.unshift(0)          
#=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.unshift(-3, -2, -1) 
#=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.shift #=> 1
numbers
#=> [2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.delete_at(2) #=> 4
numbers             
#=> [2, 3, 5, 6, 7, 8, 9, 10]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.delete(2) #=> 2
numbers           #=> [3, 5, 6, 7, 8, 9, 10]

numbers = Array.new(10) { |n| n = n * 2 } 
#=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

numbers = Array(100..110)
#=> [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]

# 或者我们可以将范围转换为数组
(100..110).to_a 
#=> [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]

arr = ['foo', 0, nil, 'bar', 7, nil]
arr.compact  #=> ['foo', 0, 'bar', 7]
arr      #=> ['foo', 0, nil, 'bar', 7, nil]
arr.compact! #=> ['foo', 0, 'bar', 7]
arr      #=> ['foo', 0, 'bar', 7]

arr = [2, 5, 6, 556, 6, 6, 8, 9, 0, 123, 556]
arr.uniq #=> [2, 5, 6, 556, 8, 9, 0, 123]

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.include? "Mars"
# 输出 => true
planets.include? "Pluto"
# 输出 => false

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.size
# 输出 => 8
planets.length
# 输出 => 8

您可以使用大小或长度，两者都是同义词

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.clear
# 输出 => []

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers[0]
# or
numbers.first
# 输出 => 1

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers[-1]
# or
numbers.last
# 输出 => 10

a = ["tom", "mot", "otm"]
b = [2, 3, 5]
a.zip(b)
# 输出
# [["tom", 2], ["mot", 3], ["otm", 5]]

primes = [7, 2, 3, 5]
primes.max_by { |p| p }
# 输出 => 7

primes = [7, 2, 3, 5]
primes.take(3)
# [7, 2, 3]

primes = [7, 2, 3, 5]
primes.fetch(3)
# 5
# Fetch will throw an error if the element does not exist
primes.fetch(10)
# (index 10 outside of array bounds: -4...4)
# or get an default value
primes.fetch(10, -1)
# -1

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 1]
numbers.uniq
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

primes = [7, 2, 3, 5]
primes.drop(3)
# [5]

primes = [7, 2, 3, 5]
primes.shift
# [2, 3, 5]

primes = [7, 2, 3, 5]
primes.pop
# [7, 2, 3]

primes = [7, 2, 3, 5]
primes.delete_at(-1)
# [7, 2, 3]

primes = [7, 2, 3, 5, 5]
primes.delete(5)
# [7, 2, 3]

salary = [399, 234, 566, 533, 233]
salary.each_with_index { |value, index| puts "#{index} #{value}" }
# 输出
# 0 399
# 1 234
# 2 566
# 3 533
# 4 233

salary = [399, 234, 566, 533, 233]
salary.each_index { |i| puts i}
# 输出
# 0
# 1
# 2
# 3
# 4

salary = [399, 234, 566, 533, 233]
salary.map { |s|  s * 10  }
# 返回
# [3990, 2340, 5660, 5330, 2330]
# 另一方面，每个都返回原始值
salary = [399, 234, 566, 533, 233]
salary.each { |s|  s * 10  }
# 返回
# [399, 234, 566, 533, 233]

salary = [399, 234, 566, 533, 233]
salary.collect { |s| s > 400 }
# 输出
# [false, false, true, true, false]

for value in [2, 3, 5, 7]
    puts value
end

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = 0
while index < planets.size
    puts "#{planets[index]}"
    index += 1
end

a = 1
star = '*'
while a <= 10
    puts star
    star += '*'
    a += 1
end

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = 0
loop do
    puts "#{planets[index]}"
    index += 1
    break if planets[index] == "Mars" or index > planets.size
end

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = planets.size - 1
until index < 0
    puts "#{planets[index]}"
    index -= 1
end

a = 1
star = '*'
until star.length > 10
    puts star
    star += '*'
    a += 1
end

10.times { puts "#{rand(1..100)}"}
# 输出
# 将打印 10 个随机数

仅仅因为你可以并不意味着你应该像这样迭代一个数组

data_sample = [2, 3, 5, 7]
data_sample.size.times { |index| puts "#{data_sample[index]}" }
# 输出
# 2
# 3
# 5
# 7

data_sample = [2, 3, 5, 7]
0.upto((data_sample.size - 1) / 2) { |index| puts "#{data_sample[index]}" }
# 输出
# 2
# 3

data_sample = [2, 3, 5, 7]
(data_sample.size - 1).downto(data_sample.size / 2) { |index| puts "#{data_sample[index]}" }
# 输出
# 7
# 5

numbers = [2, 2, 2, 2, 2]
numbers.reduce(11, :+)
# 输出
# 21

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.detect { |name| name.start_with?("E") and name.end_with?("h") }
# output
# Earth
salary = [399, 234, 566, 533, 233]
salary.detect { |s| s > 1000 }
# output
# nil

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.find { |name| name.start_with?("E") and name.end_with?("h") }
# output
# Earth

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.select { |n| n % 2 == 0 }
# 现在你有一个偶数数组
# [2, 4, 6, 8, 10]
# 如果没有满足您的逻辑的值，则返回一个空数组
[1, 1, 1].select { |n| n % 2 == 0 }
# no even numbers
# []

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.reject { |n| n % 2 == 0 }
# 如果数字是偶数则拒绝，所以现在我们有一个奇数数组
# [1, 3, 5, 7, 9]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.keep_if { |n| n % 2 == 0 }
# numbers 数组仅包含偶数
# [2, 4, 6, 8, 10]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.delete_if { |n| n % 2 == 0 }
# numbers 数组仅包含奇数
# [1, 3, 5, 7, 9]

numbers = [1, 2, 3, 1, 2, 3, 0]
numbers.drop_while { |n| n < 3 }
# 是 3 小于 3，返回 false，所以删除 1, 2
# [3, 1, 2, 3, 0]

words = %w[first second third fourth fifth sixth]
str = ""
words.reverse_each {|word| str += "#{word} "}
p str #=> "sixth fifth fourth third second first "

[2, 4, 6, 8, 10].all? { |num| num % 2 == 0 }
# true
[1, 4, 6, 8, 10].all? { |num| num % 2 == 0 }
# false

[1, 3, 5, 7, 10].any? { |num| num % 2 == 0 }
# true
[1, 3, 5, 7, 19].any? { |num| num % 2 == 0 }
# false

[1, 3, 2, 5, 7].one? { |num| num % 2 == 0 }
# true
[1, 3, 2, 5, 4].one? { |num| num % 2 == 0 }
# false

[1, 3, 5, 7, 9].none? { |num| num % 2 == 0 }
# true
[2, 3, 5, 7, 9].none? { |num| num % 2 == 0 }
# false

[].empty?
# true
[1, 3, 5, 7, 9].empty?
# false

[0, 1, 2, 3] & [1, 2] # => [1, 2]
[0, 1, 0, 1] & [0, 1] # => [0, 1]

[0, 1, 2, 3].intersection([0, 1, 2], [0, 1, 3])
# => [0, 1]
[0, 0, 1, 1, 2, 3].intersection([0, 1, 2], [0, 1, 3])
# => [0, 1]

a = [0, 1] + [2, 3]
a # => [0, 1, 2, 3]

[0, 1, 1, 2, 1, 1, 3, 1, 1] - [1] 
# => [0, 2, 3]
[0, 1, 2, 3] - [3, 0] 
# => [1, 2]
[0, 1, 2] - [4] 
# => [0, 1, 2]

[0, 1, 2, 3].union([4, 5], [6, 7]) 
# => [0, 1, 2, 3, 4, 5, 6, 7]
[0, 1, 1].union([2, 1], [3, 1]) 
# => [0, 1, 2, 3]
[0, 1, 2, 3].union([3, 2], [1, 0]) 
# => [0, 1, 2, 3]

[0, 1, 1, 2, 1, 1, 3, 1, 1].difference([1])
# => [0, 2, 3]
[0, 1, 2, 3].difference([3, 0], [1, 3])
# => [2]
[0, 1, 2].difference([4])
# => [0, 1, 2]

a = [0, 1, 2]
a1 = [3, 4]
p = a.product(a1)
p.size # => 6 # a.size * a1.size
p # => [[0, 3], [0, 4], [1, 3], [1, 4], [2, 3], [2, 4]]

# variable count
count = 4
# using while loop
# here conditional is count i.e. 4
while count >= 1
  # statements to be executed
  puts "Ruby Cheatsheet"
  count = count - 1
  # while loop ends here
end

输出

Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet

# loop using range as expression
text = "Ruby Cheatsheet"
# using for loop with the range
for count in 1..5 do
  puts text
end

输出

Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet

# starting of do..while loop
loop do
  puts "Ruby Cheatsheet"
  val = '7'
  # using boolean expressions
  if val == '7'
    break
  end
  # ending of ruby do..while loop
end

输出

Ruby Cheatsheet

var = 7
# here do is optional
until var == 11 do
  # code to be executed
  puts var * 10
  var = var + 1
  # here loop ends
end

输出

70
80
90
100

salary = [399, 234, 566, 533, 233]
salary.each do |s|
  break if s == 566
  puts s
end
# 输出
# 399
# 234

通过使用 break 关键字

salary = [399, 234, 566, 533, 233]
salary.each do |s|
  next if s == 533
  puts s
end
# 输出
# 399
# 234
# 566
# 233

通过使用 next 关键字

data = [456, 3000]
retry_count = 0
status = "network failure"
sum = 0
data.each do |d|
    if retry_count == 3
        status = "connection established"
        retry_count = 0
        redo
    elsif status == "network failure" and retry_count < 5
        puts "network failure #{retry_count}"
        retry_count += 1
        redo
    elsif status == "connection established"
        puts d
        sum += d
    end
end
# output of sum
# 3456

numbers = [2, 2, 44, 44]
sum = 0
begin
    numbers.each do |s|
        if rand(1..10) == 5
            puts "hi 5, let's do it again!"
            sum = 0
            raise "hi 5"
        end
        puts s
        sum += s
    end
rescue
    retry
end