Ruby 隐晦的 Ruby 语法：单字符的字符串
今天看 HighLine 库的源码意外发现的，语法是一个问号紧跟一个字符，等价于这个只含一个该字符的字符串：
require "minitest/autorun"
describe "?y" do
it "is the same thing as 'y'" do
?y.must_equal 'y'
end
end
翻了一下镐头书第三版，里面居然有收纳这个语法。并且给出了这样的评价：
Do yourself a favor and immediately forget this section. It’s far easier to use regular octal and hex escape sequences than to remember these ones. Use "a" rather than ?a, and use "\n" rather than ?\n.
出于装 X 的考虑，以后要找机会多用 www
这个用法是 1.9 新加的，和 1.8.7 还不兼容。
[~/work] $ ruby -v -e "p ?a"
ruby 1.8.7 (2012-02-08 patchlevel 358) [universal-darwin12.0]
97
[~/work] $ ruby -v -e "p ?a"
ruby 1.9.3p392 (2013-02-22 revision 39386) [x86_64-darwin12.3.0]
"a"
# A shortcut to HighLine.ask() a question that only accepts "yes" or "no"
# answers ("y" and "n" are allowed) and returns +true+ or +false+
# (+true+ for "yes"). If provided a +true+ value, _character_ will cause
# HighLine to fetch a single character response. A block can be provided
# to further configure the question as in HighLine.ask()
#
# Raises EOFError if input is exhausted.
#
def agree( yes_or_no_question, character = nil )
ask(yes_or_no_question, lambda { |yn| yn.downcase[0] == ?y}) do |q|
q.validate = /\Ay(?:es)?|no?\Z/i
q.responses[:not_valid] = 'Please enter "yes" or "no".'
q.responses[:ask_on_error] = :question
q.character = character
yield q if block_given?
end
end
哇，他这种写法是可以兼容 1.9 和 1.8 的.... 1.8 的 String#[] 返回 ascii，?也返回 ascii 1.9 的 String#[] 返回字符串，?也返回字符串
