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锁定老帖子 主题:ruby的to_proc
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作者 | 正文 |
发表时间:2010-10-21
最后修改:2010-11-21
引用 Method#proc
meth.to_proc => prc Returns a Proc object corresponding to this method. prc.to_proc → prc Part of the protocol for converting objects to Proc objects. Instances of class Proc simply return themselves. 2,to_proc经常和&一起使用. 可以把block传递给带block的方法.block的to_proc返回的就是本身. 如果对象自带to_proc方法的话,就可以把它当作带"&"的参数传给带block方法(默认状态下,Proc、Method对象都有to_proc方法)。方法调用时会执行to_proc,它将返回Proc对象. pobj = lambda {|v| p v } [1,2,3].each(&pobj) => 1 2 3 class Foo def to_proc lambda {|v| p v} end end [1,2,3].each(&Foo.new) => 1 2 3 class Symbol def to_proc proc { |obj, *args| obj.send(self, *args) } end end projects.collect(&:name) [1, 2, 3].map(&:to_s.to_proc) #=> ["1", "2", "3"] class Person < ActiveRecord::Base; end; [{:name => 'Dan'}, {:name => 'Josh'}].map(&Person.method(:new)) class Class def to_proc proc(&method(:new)) end end [{:name => 'Dan'}, {:name => 'Josh'}].map(&Person) 3,to_proc和method_missing module Kernel protected def it() It.new end alias its it end class It undef_method(*(instance_methods - %w*__id__ __send__*)) def initialize @methods = [] end def method_missing(*args, &block) @methods << [args, block] unless args == [:respond_to?, :to_proc] self end def to_proc lambda do |obj| @methods.inject(obj) do |current,(args,block)| current.send(*args, &block) end end end end File.read("/etc/passwd").split.sort_by &it.split(":")[2] User.find(:all).map &its.contacts.map(&its.last_name.capitalize) 4,Going crazy 可以让&使用多个参数,更性感。 What I always regretted though was not being to pass any arguments, so I hacked and monkeypatched a bit, and got: class Symbol def with(*args, &block) @proc_arguments = { :args => args, :block => block } self end def to_proc @proc_arguments ||= {} args = @proc_arguments[:args] || [] block = @proc_arguments[:block] @proc_arguments = nil Proc.new { |obj, *other| obj.send(self, *(other + args), &block) } end end #So you can now write: some_dates.map(&:strftime.with("%d-%M-%Y")) Not that this is any shorter than just creating the darn block in the first place. But hey, it’s a good exercise in metaprogramming and show of more of Ruby’s awesome flexibility. After this I remembered something similar that annoyed me before. It’s that Rails helper methods are just a bag of methods available to, because they are mixed in your template. So if you have an array of numbers that you want to format as currency, you’d have to do: <%= @prices.map { |price| number_to_currency(price) }.to_sentence %> What if I could apply some to_proc-love to that too? All these helper methods cannot be added to strings, fixnums, and the likes; that would clutter way to much. Rather, it might by a nice idea to use procs that understands helper methods. Here is what I created: module ProcProxyHelper def it(position = 1) ProcProxy.new(self, position) end class ProcProxy instance_methods.each { |m| undef_method(m) unless m.to_s =~ /^__|respond_to\?|method_missing/ } def initialize(object, position = 1) @object, @position = object, position end def to_proc raise "Please specify a method to be called on the object" unless @delegation Proc.new { |*values| @object.__send__(*@delegation[:args].dup.insert(@position, *values), &@delegation[:block]) } end def method_missing(*args, &block) @delegation = { :args => args, :block => block } self end end end I used a clean blank class (in Ruby 1.9, you’d want to inherit it from BasicObject), in which I will provide the proper proc-object. I play around with the argument list a bit, handling multiple arguments and blocks too. You can now use this syntax: <%= @prices.map(&it.number_to_currency).to_sentence %> That is a lot sexier if you as me. And you can use it in any object, not just inside views. And lets add some extra arguments and some Enumerator-love too: class SomeClass include ProcProxyHelper def initialize(name, list) @name, @list = name, list end def apply(value, index, seperator) "#{@name}, #{index} #{separator} #{value}" end def applied_list @list.map.with_index(&it.apply(":")) end end In case you are wondering, the position you can specify is to tell where the arguments need to go. Position 0 is the method name, so you shouldn’t use that, but any other value is okay. An example might be that you cant to wrap an array of texts into span-tags: <%= some_texts.map(&it(2).content_tag(:span, :class => "foo")).to_sentence %> So there you have it. I’m probably solving a problem that doesn’t exist. It is however a nice example of the awesome power of Ruby. I hope you’ve enjoyed this little demonstration of the possible uses of to_proc. 最后的一部分来自于http://iain.nl/2010/02/going-crazy-with-to_proc/ 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。
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