操作符 #

常用操作符 #

数学计算不支持 ++ 操作

puts 3 + 2 < 5 -7 # => false
x = 10
x += 1
puts x  # => 11

puts(2 ** 3) # => 8
puts(9 / 3) # => 3

逻辑操作

puts true and 1 == 2 # => true
puts true && 1 == 2 # => false
puts true or 1 == 2 # => true
puts true || 1 == 2 # => true
puts !true # => false
puts (not (1==1)) # => false
puts 3 > 2 ? '3>2' : '3<=2' # => 3>2

条件赋值

参数为空时进行赋值

favorite_book ||= "Cat's Cradle"

相等性 #

== 比较的是内容

puts 1 == 1 # => true
puts 1 != 2 # => true
puts "foo" == "foo" # => true

比较数字

puts 1 == 1.0 # => true
puts 1.eql? 1.0 # => false

比较对象

foo = 'foo'
foo_dup = foo.dup
puts foo == foo_dup # => true
puts foo.equal? foo_dup # => false

比较器 #

比较器返回的是整形数字，使用符号 <==>

book_1 = 'A Wrinkle in Time'
book_2 = 'A Brief History of Time'
puts book_1 <=> book_2  # => 1

比较器可以用在排序中

books = ['Charlie and the Chocolate Factory', 'War and Peace', 'Utopia', 'A Brief History of Time', 'A Wrinkle in Time']
puts books.sort! { |firstBook, secondBook| firstBook <=> secondBook }

defined? #

defined? 用于判断一个变量或函数是否被定义，如果定义了则返回对应的描述字符串（如 local variable, global variable），否则返回空。

puts defined? foo # => local-variable
puts defined? puts  # => method

BEGIN 与 END #

BEGIN 与 END 可以用于定义在程序运行前后执行的代码块，即实现 hook 功能。

BEGIN {
  puts 'setUp'
}
END {
  puts 'tearDown'
}

BEGIN 与 END 可以定义多个，BEGIN 按照定义的顺序执行，END 则相反，定义在后面的先执行。

BEGIN {
  puts 'setUp01'
}
BEGIN {
  puts 'setUp02'
}
BEGIN {
  puts 'setUp03'
}
END {
  puts 'tearDown01'
}
END {
  puts 'tearDown02'
}
END {
  puts 'tearDown03'
}

以上代码会输出

setUp01
setUp02
setUp03
tearDown03
tearDown02
tearDown01