浏览 5499 次
锁定老帖子 主题:只想与你深发展..
该帖已经被评为良好帖
|
|
---|---|
作者 | 正文 |
发表时间:2009-06-14
引用 自从深发展银行推出那条知性的广告语“只想与你深发展”后,银行业内人士又自编出了更知性的姊妹篇:“光大是不行的” 正题:研究一下ruby中深拷贝(deep clone)的问题。 1.= ruby里拷贝对象的最简单方法,下面来看一下效果: irb(main):002:0> a = "Hooopo" => "Hooopo" irb(main):003:0> b = a => "Hooopo" irb(main):004:0> b.object_id => 23424840 irb(main):005:0> a.object_id => 23424840 irb(main):006:0> b.gsub!("o","-") => "H---p-" irb(main):007:0> p a "H---p-" => nil irb(main):008:0> p b "H---p-" => nil b修改后,a也跟着修改了,并且a和b的object_id一样,就是同一个对象嘛~ 2.dup和clone(dup和clone差不多,但是还是有一些区别的) irb(main):001:0> a = "Hooopo" => "Hooopo" irb(main):002:0> b = a.dup => "Hooopo" irb(main):003:0> a.object_id => 23428740 irb(main):004:0> b.object_id => 23425010 irb(main):005:0> b.gsub!("o","-") => "H---p-" irb(main):006:0> p b "H---p-" => nil irb(main):007:0> p a "Hooopo" => nil irb(main):008:0> b和a是不同对象,并且改变b后a不改变。这是我们想要的。但是别高兴太早,看下面例子: class Klass attr_accessor :str end s1 = Klass.new s1.str = "Hooopo" p s1 s2 = s1.dup p s2 s2.str.gsub!("o","-") p s1 p s2 #results #<Klass:0x2d2cd30 @str="Hooopo"> #<Klass:0x2d2cc7c @str="Hooopo"> #<Klass:0x2d2cd30 @str="H---p-"> #<Klass:0x2d2cc7c @str="H---p-"> 显然,问题又有了,改变s2后s1也跟着改变了。同样的陷阱也发生在Array和Hash里,看下面代码: irb(main):008:0> arr = [1,[1,1]] => [1, [1, 1]] irb(main):009:0> arr_dup = arr.dup => [1, [1, 1]] irb(main):010:0> arr_dup[0] = 2 => 2 irb(main):011:0> arr => [1, [1, 1]] irb(main):012:0> arr_dup[1][0] = 2 => 2 irb(main):013:0> arr => [1, [2, 1]] 在第一次给arr_dup[0]复值的时候arr没有改变,而第二次改变arr_dup[1][0]的时候arr也跟着改变了。就是说Array#dup只拷贝了一层,还不够深入呀..同样Hash也是,看下面代码: irb(main):001:0> hash = {:key => {:key => "value"}} => {:key=>{:key=>"value"}} irb(main):002:0> hash_dup = hash.dup => {:key=>{:key=>"value"}} irb(main):003:0> hash_dup[:key][:key] = "value_changed" => "value_changed" irb(main):004:0> hash_dup => {:key=>{:key=>"value_changed"}} irb(main):005:0> hash => {:key=>{:key=>"value_changed"}} 3.用序列化实现深拷贝 irb(main):014:0> arr = [1,[1,1]] => [1, [1, 1]] irb(main):015:0> arr_dump = Marshal.load(Marshal.dump(arr)) => [1, [1, 1]] irb(main):016:0> arr_dump.object_id => 22807940 irb(main):017:0> arr.object_id => 22850200 irb(main):018:0> arr_dump[1][1] = 2 => 2 irb(main):019:0> arr_dump => [1, [1, 2]] irb(main):020:0> arr => [1, [1, 1]] irb(main):012:0> hash = {:key => {:key => "value"}} => {:key=>{:key=>"value"}} irb(main):013:0> hash_dump = Marshal.load(Marshal.dump(hash)) => {:key=>{:key=>"value"}} irb(main):014:0> hash.object_id => 22790990 irb(main):015:0> hash_dump.object_id => 22755440 irb(main):016:0> hash_dump[:key][:key] = "value not changed" => "value not changed" irb(main):017:0> hash => {:key=>{:key=>"value"}} irb(main):018:0> hash_dump => {:key=>{:key=>"value not changed"}} 情况似乎好多了。但是还有一个问题,就是Marshal只能序列化一般对象,数组哈希,高级一些的对象不能序列化(IO,Proc,singleton等) 下面是两个deep clone的实现(via:http://www.artima.com/forums/flat.jsp?forum=123&thread=40913) class Object def deep_clone Marshal::load(Marshal.dump(self)) end end class Object def dclone case self when Fixnum,Bignum,Float,NilClass,FalseClass, TrueClass,Continuation klone = self when Hash klone = self.clone self.each{|k,v| klone[k] = v.dclone} when Array klone = self.clone klone.clear self.each{|v| klone << v.dclone} else klone = self.clone end klone.instance_variables.each {|v| klone.instance_variable_set(v, klone.instance_variable_get(v).dclone) } klone end end 更复杂的(via:http://d.hatena.ne.jp/pegacorn/20070417/1176817721)... class Object def deep_clone _deep_clone({}) end protected def _deep_clone(cloning_map) return cloning_map[self] if cloning_map.key? self cloning_obj = clone cloning_map[self] = cloning_obj cloning_obj.instance_variables.each do |var| val = cloning_obj.instance_variable_get(var) begin val = val._deep_clone(cloning_map) rescue TypeError next end cloning_obj.instance_variable_set(var, val) end cloning_map.delete(self) end end class Array protected def _deep_clone(cloning_map) return cloning_map[self] if cloning_map.key? self cloning_obj = super cloning_map[self] = cloning_obj cloning_obj.map! do |val| begin val = val._deep_clone(cloning_map) rescue TypeError # end val end cloning_map.delete(self) end end class Hash protected def _deep_clone(cloning_map) return cloning_map[self] if cloning_map.key? self cloning_obj = super cloning_map[self] = cloning_obj pairs = cloning_obj.to_a cloning_obj.clear pairs.each do |pair| pair.map! do |val| begin val = val._deep_clone(cloning_map) rescue TypeError # end val end cloning_obj[pair[0]] = pair[1] end cloning_map.delete(self) end end Something about dup and clone 1.ruby字面量(Fixnum,true,false,nil,Symbol)不可以调用dup和clone方法,会报TypeError。 2.对对象的state(taint,frozen)的改变:dup会把frozen的对象unfrozen,clone不会。 irb(main):019:0> o = Object.new => #<Object:0x2b7855c> irb(main):020:0> o.taint => #<Object:0x2b7855c> irb(main):021:0> o.freeze => #<Object:0x2b7855c> irb(main):024:0> [o.frozen?,o.tainted?] => [true, true] irb(main):025:0> o_clone = o.clone => #<Object:0x2b44c0c> irb(main):026:0> [o_clone.frozen?,o_clone.tainted?] => [true, true] irb(main):027:0> o_dup = o.dup => #<Object:0x2b32e6c> irb(main):028:0> [o_dup.frozen?,o_dup.tainted?] => [false, true] 3.对单体方法的拷贝:clone会连同单体方法一起拷贝,dup不会。 irb(main):029:0> o = Object.new => #<Object:0x2b256a4> irb(main):030:0> def o.say irb(main):031:1> puts "Hello,Hooopo" irb(main):032:1> end => nil irb(main):033:0> o_dup = o.dup => #<Object:0x296acec> irb(main):035:0> o_clone = o.clone => #<Object:0x2dba194> irb(main):037:0> o_dup.say NoMethodError: undefined method `say' for #<Object:0x296acec> from (irb):37 from :0 irb(main):038:0> o_clone.say Hello,Hooopo 声明:ITeye文章版权属于作者,受法律保护。没有作者书面许可不得转载。
推荐链接
|
|
返回顶楼 | |
发表时间:2009-06-14
Array、Hash、实例变量 已经足够表达数据结构了。 data 易 dump,class 不易 dump ……
现在最想要的是 Binding 和 Proc 的 Marshal.dump, 或者 dump module 也行…… |
|
返回顶楼 | |
发表时间:2009-06-14
night_stalker 写道
Array、Hash、实例变量 已经足够表达数据结构了。 data 易 dump,class 不易 dump ……
现在最想要的是 Binding 和 Proc 的 Marshal.dump, 或者 dump module 也行……
|
|
返回顶楼 | |
发表时间:2009-06-14
http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/8c08df930291a2e9/3cccf36faad55d8c?hl=zh-cn&lnk=gst&q=dump+module#3cccf36faad55d8c
How about the following? The only major disadvantage is that it will be a little bit slower than using a real Proc: require 'delegate' class DumpableProc < DelegateClass(Proc) def initialize(str) eval "@proc = proc { #{str} }" @str = str super(@proc) end def _dump(limit) @str end def self._load(str) self.new(str) end end dp = DumpableProc.new("puts 'foo!'") dp.call() dump_str = Marshal.dump(dp) puts dump_str dp2 = Marshal.load(dump_str) dp2.call() |
|
返回顶楼 | |
发表时间:2009-06-14
1.8 可以用:
require 'ruby2ruby' module X def x 'x' end end Ruby2Ruby.translate X #=> "module X\n def x\n \"x\"\n end\nend" 但是 1.9 不能用…… |
|
返回顶楼 | |
发表时间:2009-12-10
最后修改:2009-12-10
Hooopo分析真是透彻。看下api。
Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference. dup copies the tainted state of obj. See also the discussion under Object#clone. In general, clone and dup may have different semantics in descendent classes. While clone is used to duplicate an object, including its internal state, dup typically uses the class of the descendent object to create the new instance. 分析下。 1,Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference. 借用下Hooopo的代码。希望不要介意。 irb(main):001:0> a = "Hooopo" => "Hooopo" irb(main):002:0> b = a.dup => "Hooopo" irb(main):003:0> a.object_id => 23428740 irb(main):004:0> b.object_id => 23425010 irb(main):005:0> b.gsub!("o","-") => "H---p-" irb(main):006:0> p b "H---p-" => nil irb(main):007:0> p a "Hooopo" => nil irb(main):008:0> b对象,存储的"Hooopo",b改变,所以a不会变。 class Klass attr_accessor :str end s1 = Klass.new s1.str = "Hooopo" p s1 s2 = s1.dup p s2 s2.str.gsub!("o","-") p s1 p s2 #results #<Klass:0x2d2cd30 @str="Hooopo"> #<Klass:0x2d2cc7c @str="Hooopo"> #<Klass:0x2d2cd30 @str="H---p-"> #<Klass:0x2d2cc7c @str="H---p-"> s1,s2虽然是不同的对象,但是对象内储的却是Klass一个实例的地址。所以会改变。 irb(main):008:0> arr = [1,[1,1]] => [1, [1, 1]] irb(main):009:0> arr_dup = arr.dup => [1, [1, 1]] irb(main):010:0> arr_dup[0] = 2 => 2 irb(main):011:0> arr => [1, [1, 1]] irb(main):012:0> arr_dup[1][0] = 2 => 2 irb(main):013:0> arr => [1, [2, 1]] attr数组内存储的是1和[2,1]的地址,所以attr[0]改变不会受影响,而attr[1]则会受影响。 2,While clone is used to duplicate an object, including its internal state, dup typically uses the class of the descendent object to create the new instance. 最后这句是关键。clone是在复制对象,包括对象的状态,而dup则是从其派生类创建一个新的实例。所以对于attr=[1, [1, 1]],attr[0]存的是integer,会创建integer类型,attr[1]是一个数组类型,dup只能简单的复制attr[1]中用来保存[1,1]的地址的类的一个新实例。 对于hash,或者更复杂的类,我想原理应该是相同的。 有什么不对的,还希望能指出来。 |
|
返回顶楼 | |