我使用这段代码让用户输入名称，而程序将它们存储在一个数组中，直到他们输入一个空字符串(他们必须在每个名称后按enter):
people = []
info = 'a' # must fill variable with something, otherwise loop won't execute
while not info.empty?
info = gets.chomp
people += [Person.new(info)] if not info.empty?
end
这段代码在do…while循环:
people = []
do
info = gets.chomp
people += [Person.new(info)] if not info.empty?
while not info.empty?
在这段代码中，我不需要将信息分配给一些随机字符串。
不幸的是，Ruby中似乎不存在这种类型的循环。谁能提出一个更好的方法来做这件事?
当前回答
这个怎么样?
people = []
until (info = gets.chomp).empty?
people += [Person.new(info)]
end
其他回答
I found the following snippet while reading the source for Tempfile#initialize in the Ruby core library: begin tmpname = File.join(tmpdir, make_tmpname(basename, n)) lock = tmpname + '.lock' n += 1 end while @@cleanlist.include?(tmpname) or File.exist?(lock) or File.exist?(tmpname) At first glance, I assumed the while modifier would be evaluated before the contents of begin...end, but that is not the case. Observe: >> begin ?> puts "do {} while ()" >> end while false do {} while () => nil As you would expect, the loop will continue to execute while the modifier is true. >> n = 3 => 3 >> begin ?> puts n >> n -= 1 >> end while n > 0 3 2 1 => nil While I would be happy to never see this idiom again, begin...end is quite powerful. The following is a common idiom to memoize a one-liner method with no params: def expensive @expensive ||= 2 + 2 end Here is an ugly, but quick way to memoize something more complex: def expensive @expensive ||= begin n = 99 buf = "" begin buf << "#{n} bottles of beer on the wall\n" # ... n -= 1 end while n > 0 buf << "no more bottles of beer" end end
原作者:Jeremy Voorhis这里的内容是复制的，因为它似乎是从原始站点删除的。副本也可以在Web Archive和Ruby Buzz论坛上找到。——蜥蜴比尔
这是hubbardr的死链接到我博客的全文文章。
我在Ruby核心库中读取Tempfile#initialize的源代码时发现了以下代码片段:
begin
tmpname = File.join(tmpdir, make_tmpname(basename, n))
lock = tmpname + '.lock'
n += 1
end while @@cleanlist.include?(tmpname) or
File.exist?(lock) or File.exist?(tmpname)
乍一看，我以为while修饰符会在begin…结束，但事实并非如此。观察:
>> begin
?> puts "do {} while ()"
>> end while false
do {} while ()
=> nil
正如您所期望的那样，当修饰符为true时，循环将继续执行。
>> n = 3
=> 3
>> begin
?> puts n
>> n -= 1
>> end while n > 0
3
2
1
=> nil
虽然我很高兴再也不会看到这个习语，但开始吧……End是非常强大的。下面是一个常用的习语来记住没有参数的一行方法:
def expensive
@expensive ||= 2 + 2
end
下面是一个丑陋但快速记住更复杂事物的方法:
def expensive
@expensive ||=
begin
n = 99
buf = ""
begin
buf << "#{n} bottles of beer on the wall\n"
# ...
n -= 1
end while n > 0
buf << "no more bottles of beer"
end
end
a = 1
while true
puts a
a += 1
break if a > 10
end
现在可以正常工作了:
begin
# statment
end until <condition>
但是，它可能在将来被删除，因为begin语句是违反直觉的。参见:http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/6745
Matz (Ruby的创造者)建议这样做:
loop do
# ...
break if <condition>
end
是这样的:
people = []
begin
info = gets.chomp
people += [Person.new(info)] if not info.empty?
end while not info.empty?
参考:Ruby的Hidden do {} while()循环
