红宝石 |日期 <<函数
Date#<<()是一个 Date 类方法，它返回指向 self 前几个月的“n”（数值参数）的日期对象。
Syntax: Date.<<()
Parameter: Date values
Return: date object pointing n months before self. The argument n should be a numeric value.
示例 #1：
# Ruby code for Date.<<() method
# loading date
require 'date'
# declaring Date
a = Date.new(2019, 1, 1)
# declaring Date
b = Date.jd(2452004)
# declaring Date
c = Date.ordinal(2019, 12)
# Date
puts "Date a : #{a}\n\n"
puts "Date b : #{b}\n\n"
puts "Date c : #{c}\n\n\n\n"
# << form
puts "Date a << form : #{a << Rational(3, 2)}\n\n"
puts "Date b << form : #{b << Rational(10, 2)}\n\n"
puts "Date c << form : #{c << Rational(10, 4)}\n\n"
输出 ：
Date a : 2019-01-01
Date b : 2001-04-04
Date c : 2019-01-12
Date a << form : 2018-11-01
Date b << form : 2000-11-04
Date c << form : 2018-10-12
示例 #2：
# Ruby code for Date.<<() method
# loading date
require 'date'
# declaring Date
a = Date.parse('2019-01-01')
# declaring Date
b = Date.strptime('03-12-2019', '%d-%m-%Y')
# declaring Date
c = Date.commercial(2019, 5, 6)
# Date
puts "Date a : #{a}\n\n"
puts "Date b : #{b}\n\n"
puts "Date c : #{c}\n\n\n\n"
# << form
puts "Date a << form : #{a << Rational(3, 2)}\n\n"
puts "Date b << form : #{b << Rational(10, 2)}\n\n"
puts "Date c << form : #{c << Rational(10, 4)}\n\n"
输出 ：
Date a : 2019-01-01
Date b : 2019-12-03
Date c : 2019-02-02
Date a << form : 2018-11-01
Date b << form : 2019-07-03
Date c << form : 2018-11-02