是否存在與String.next相反的內容？

Question

Ruby中的next與之相反的是什麼？ 我試圖找到一個不存在的函數，如prev。

"b".prev將== "a"，就像"a".next == "b"

# A grad student at a local university thinks he has discovered a formula to 
# predict what kind of grades a person will get. He says if you own less than 
# 10 books, you will get a "D". If you own 10 to 20 books, you will get a "C", 
# and if you own more than 20 books, you will get a "B". 
# He further hypothesizes that if you actually read your books, then you will 
# get a full letter grade higher in every case. 
# 
# grade(4, false) # => "D" 
# grade(4, true) # => "C" 
# grade(15, true) # => "B" 

Answer 1

如果你的情況是有限的，以獨特的性格下面將讓你得到以前 或下一個字符：

def next_char(c) 
    (c.chr.ord + 1).chr 
end 

def prev_char(c) 
    (c.chr.ord - 1). chr 
end 

puts next_char('A') 
puts prev_char('B') 

但是，當你處理成績時，我會選擇一個等級的枚舉。例如，看看blog post可能的實現。

編號：

• String.chr
• String.ord
• Integer.chr