最初的所謂Ruby元編程是一種可以在運行時動態(tài)地操縱語言結(jié)構(gòu)的技術(shù)，您甚至可以輸入一個新的Ruby代碼并在運行時執(zhí)行它，而無需重新啟動它，需要的朋友可以進入下文參考一下。
示例
我們有類Legislator class，現(xiàn)在，想要給它加一個find_by_first_name('John')的動態(tài)調(diào)用。實現(xiàn)find(:first_name => 'John')的功能。
復(fù)制代碼 代碼如下:
class Legislator
? #假設(shè)這是一個真實的實現(xiàn)
? def find(conditions = {})
? end
?
? #在本身定義畢竟這是他的方法
? def self.method_missing(method_sym, *arguments, &block)
??? # the first argument is a Symbol, so you need to_s it if you want to pattern match
??? if method_sym.to_s =~ /^find_by_(.*)$/
????? find($1.to_sym => arguments.first)
??? else
????? super
??? end
? end
end
?
那么這個時候調(diào)用
?
復(fù)制代碼 代碼如下:
Legislator.respond_to?(:find_by_first_name)?
?
將會提示錯誤，那么繼續(xù)
復(fù)制代碼 代碼如下:
class Legislator
? # 省略
?
? # It's important to know Object defines respond_to to take two parameters: the method to check, and whether to include private methods
? # http://www.
ruby-doc.org/core/classes/Object.html#M000333
? def self.respond_to?(method_sym, include_private = false)
??? if method_sym.to_s =~ /^find_by_(.*)$/
????? true
??? else
????? super
??? end
? end
end
?
正如代碼注釋所述respond_to?需要兩個參數(shù)，如果，你沒有提供將會產(chǎn)生ArgumentError。
相關(guān)反射 DRY
如果我們注意到了這里有重復(fù)的代碼。我們可以參考ActiveRecord的實現(xiàn)封裝在ActiveRecord::DynamicFinderMatch，以便避免在method_missing和respond_to?中重復(fù)。
復(fù)制代碼 代碼如下:
class LegislatorDynamicFinderMatch
? attr_accessor :attribute
? def initialize(method_sym)
??? if method_sym.to_s =~ /^find_by_(.*)$/
????? @attribute = $1.to_sym
??? end
? end
?
? def match?
??? @attribute != nil
? end
end
?
class Legislator
? def self.method_missing(method_sym, *arguments, &block)
??? match = LegislatorDynamicFinderMatch.new(method_sym)
??? if match.match?
????? find(match.attribute => arguments.first)
??? else
????? super
??? end
? end
? def self.respond_to?(method_sym, include_private = false)
??? if LegislatorDynamicFinderMatch.new(method_sym).match?
????? true
??? else
????? super
??? end
? end
end
?
緩存 method_missing
重復(fù)多次的method_missing可以考慮緩存。
另外一個我們可以向ActiveRecord 學(xué)習的是，當定義method_missing的時候，發(fā)送 now-defined方法。如下：
復(fù)制代碼 代碼如下:
class Legislator???
? def self.method_missing(method_sym, *arguments, &block)
??? match = LegislatorDynamicFinderMatch.new(method_sym)
??? if match.match?
????? define_dynamic_finder(method_sym, match.attribute)
????? send(method_sym, arguments.first)
??? else
????? super
??? end
? end
?
? protected
?
? def self.define_dynamic_finder(finder, attribute)
??? class_eval <<-RUBY
????? def self.#{finder}(#{attribute})??????? # def self.find_by_first_name(first_name)
??????? find(:#{attribute} => #{attribute})?? #?? find(:first_name => first_name)
????? end???????????????????????????????????? # end
??? RUBY
? end
end
?
測試
測試部分如下：
復(fù)制代碼 代碼如下:
describe LegislatorDynamicFinderMatch do
? describe 'find_by_first_name' do
??? before do
????? @match = LegislatorDynamicFinderMatch.new(:find_by_first_name)
??? end
?????
??? it 'should have attribute :first_name' do
????? @match.attribute.should == :first_name
??? end
???
??? it 'should be a match' do
????? @match.should be_a_match
??? end
? end
?
? describe 'zomg' do
??? before do
????? @match = LegislatorDynamicFinderMatch(:zomg)
??? end
???
??? it 'should have nil attribute' do
????? @match.attribute.should be_nil
??? end
???
??? it 'should not be a match' do
????? @match.should_not be_a_match
??? end
? end
end
?
下面是 RSpec 例子:
?
復(fù)制代碼 代碼如下:
describe Legislator, 'dynamic find_by_first_name' do?
? it 'should call find(:first_name => first_name)' do?
??? Legislator.should_receive(:find).with(:first_name => 'John')?
?????
??? Legislator.find_by_first_name('John')?
? end?
end
大家看完上文ruby元編程之創(chuàng)建自己的動態(tài)方法之后，知道要怎么操作了吧！總之，為了讓我們在工作中能順利，要多關(guān)注武林技術(shù)頻道分享的內(nèi)容哦！
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