如何使用CSS3选择器选择除最后一个孩子之外的所有孩子？

例如,只获得最后一个孩子div:nth-last-child(1).

是def greet; puts "hello"; end在Ruby中在一行上定义方法的唯一方法吗？

在那里的YAML或JSON中是否有语言代码列表？

另一种格式很好,我可以在必要时进行转换.

%w[ ]   Non-interpolated Array of words, separated by whitespace
%W[ ]   Interpolated Array of words, separated by whitespace

用法:

p %w{one one two three 0 1 1 2 3} # = > ["one", "one", "two", "three", "0", "1", "1", "2", "3"]
p %W{one one two three 0 1 1 2 3} # = > ["one", "one", "two", "three", "0", "1", "1", "2", "3"]
p %w{C:\ C:\Windows} # => ["C: C:\\Windows"]
p %W{C:\ C:\Windows} # => ["C: C:Windows"]

我的问题是......有什么区别？

当有一个可以同时处理这两个类的类时,拥有Date和Time类的目的是什么DateTime？

使用RVM,我尝试在安装Fedora 15后安装ree-1.8.7-2011.03,我收到以下错误.rvm install ree-1.8.7-2011.03在Ubuntu 11.04上使用工作正常..

与Fedora 15上的MRI ruby​​-1.8.7-p334相同的错误(和解决方案).

关于如何解决这个问题的任何想法？

make[1]: Entering directory `/home/ryguy/.rvm/src/ree-1.8.7-2011.03/source/ext/dl'
gcc -I/opt/local/include -I. -I/opt/local/include -I../.. -I../../. -I../.././ext/dl -DHAVE_DLFCN_H -DHAVE_DLOPEN -DHAVE_DLCLOSE -DHAVE_DLSYM -DHAVE_DLERROR    -I. -fPIC -g -O2   -fno-defer-pop -fno-omit-frame-pointer  -c ptr.c
gcc -I/opt/local/include -I. -I/opt/local/include -I../.. -I../../. -I../.././ext/dl -DHAVE_DLFCN_H -DHAVE_DLOPEN -DHAVE_DLCLOSE -DHAVE_DLSYM -DHAVE_DLERROR    -I. -fPIC -g -O2   -fno-defer-pop -fno-omit-frame-pointer  -c handle.c
Generating callback.func
Generating cbtable.func
gcc -I/opt/local/include -I. -I/opt/local/include -I../.. -I../../. -I../.././ext/dl -DHAVE_DLFCN_H -DHAVE_DLOPEN -DHAVE_DLCLOSE -DHAVE_DLSYM -DHAVE_DLERROR    -I. -fPIC -g -O2   -fno-defer-pop -fno-omit-frame-pointer  -c dl.c
In …

我将如何在Ruby中执行此操作？

p "abc".all_possible_permutations

会回来:

[
  "abc",
  "acb",
  "bca",
  "bac",
  "cba",
  "cab",
]

编辑

感谢Jakub Hampl:

class String
  def all_possible_permutations
    self.chars.to_a.permutation.map(&:join)
  end
end

尝试在Ruby中使用基础...我已经列出的代码似乎非常重复.还有更好的方法吗？

module Converter
  def self.convert(value, from, to)
    case from
    when :hex
      case to
      when :dec
        # code to change hex to dec
      when :oct
        # code to change hex to oct
      when :bin
        # code to change hex to bin
      when :ascii
        # code to change hex to ascii
      end
    when :dec
      case to
      when :hex
        # code to change dec to hex
      when :oct
        # code to change dec to oct
      when :bin
        # code to change dec to …

这是一个真实的快速示例:

puts File.join(nil, "hello")

会输出

test.rb:4:in 'join': can't convert nil into String (TypeError)
from test.rb:4

但是当我这样做时:

begin
  puts File.join(nil, "hello")
rescue => exception
  puts exception.backtrace
end

这将输出

test.rb:4:in 'join'
test.rb:4

现在我如何捕获完整的回溯,包括"无法将nil转换为String(TypeError)"部分？

@Sarah Vessels: 在我的特定代码中,这段代码:

puts "=============================="
puts error.message
puts "=============================="
puts error.inspect
puts "=============================="
puts error.backtrace
puts "=============================="

回报

==============================
exit
==============================
#<SystemExit: exit>
==============================
/usr/lib/ruby/1.8/glib2.rb:37:in `exit'
/usr/lib/ruby/1.8/glib2.rb:37:in `exit_application'
multi.rb:234:in `main'
multi.rb:347
==============================

在Ruby中,您可以使用数组上的map/collect方法对其进行修改:

a = [ "a", "b", "c", "d" ]
a.collect! {|x| x + "!" }
a                            #=>  [ "a!", "b!", "c!", "d!" ]

在C#中有一种简单的方法吗？