如何建立鏈式方法，如 - should_receive（：something）.with（：params，values）.and_return（：something_else）

Question

我試圖讓我的代碼稍微小一點，構建一個方法，看起來像來自RSpec的should_receive ，這裏的情況是，我測試的狀態機，我有幾種方法有這樣的代碼：

context "State is unknown" do 
    before do 
    @obj = create_obj(:state => 'unknown') 
    end 
    context "Event add" do 
    it 'should transition to adding if not in DB' do 
     @obj.add 
     @obj.state.should == 'adding' 
    end 

    it 'should transition to linking if already in DB' do 
     create_obj_in_db 
     @obj.add 
     @obj.state.should == 'linking' 
    end 
    end 
end 

我想這幾行代碼來代替類似於這樣：

@obj.should_receive(:add).and_transition_to('adding') 
@obj.should_receive(:modify).and_transition_to('modifying') 

這些方法是如何構建的？

Answer 1

到鏈的重要組成部分，是從物體返回self，所以下次調用仍然可以在工作目的。

class Foo 
    def one 
    puts "one" 
    self 
    end 

    def two 
    puts "two" 
    self 
    end 

    def three 
    puts "three" 
    self 
    end 
end 

a=Foo.new 
a.one.two.three 

Answer 2

它不是ruby-on-rails，但this article給出了一個Fluent Interface的示例。

public class Pipeline 
{ 
    private Image image; 
    public Image CurrentImage 
    { 
     get { return image; } 
     set { image = value; } 
    } 

    public Pipeline(string inputFilename) 
    { 
     image = Bitmap.FromFile(inputFilename); 
    } 

    public Pipeline Rotate(float Degrees) 
    { 
     RotateFilter filter = new RotateFilter(); 
     filter.RotateDegrees = Degrees; 
     image = filter.ExecuteFilter(image); 
     return this; 
    } 
    : 

Answer 3

簡單：

 
class Obj 
    def should_receive(msg) 
    self.send(msg.to_sym) 
    self 
    end 
    def and_transition_to(state) 
    @state == state 
    end 
    def add 
    @state = 'adding' 
    end 
end 

現在你可以運行：

 
obj = Obj.new 
obj.should_receive(:add).and_transition_to('adding') 
=> true