重複切換語句所需的重構

Question

許多重複的切換語句似乎需要進行DRY'd。有什麼建議麼？ （包括做什麼！）

AnimMapIter _iter; 
    _iter = _animations->find(name); 
    if(_iter == _animations->end()) return; 

    if(_curName != name) { 
     _curName = name; 

     switch(dir) { 
     case DIR_FORWARD_LOOPING: /* Fall through to DIR_FORWARD_NONLOOPING */ 
     case DIR_FORWARD_NONLOOPING: 
      _iter->second->First(); 
      break; 
     case DIR_REVERSE_LOOPING: /* Fall through to DIR_REVERSE_NONLOOPING */ 
     case DIR_REVERSE_NONLOOPING: 
      _iter->second->Last(); 
      break; 
     } 
    } else { 

     switch(dir) { 
     case DIR_FORWARD_LOOPING: /* Fall through to DIR_FORWARD_NONLOOPING */ 
     case DIR_FORWARD_NONLOOPING: 
      _iter->second->Next(); 
      break; 
     case DIR_REVERSE_LOOPING: /* Fall through to DIR_REVERSE_NONLOOPING */ 
     case DIR_REVERSE_NONLOOPING: 
      _iter->second->Previous(); 
      break; 
     } 

     switch(dir) { 
      case DIR_FORWARD_LOOPING: 
       if(_iter->second->IsAtEnd()) 
        _iter->second->First(); 
       break; 
      case DIR_FORWARD_NONLOOPING: 
       if(_iter->second->IsAtEnd()) 
        _iter->second->Last(); 
       break; 
      case DIR_REVERSE_LOOPING: 
       if(_iter->second->IsAtFront()) 
        _iter->second->Last(); 
       break; 
      case DIR_REVERSE_NONLOOPING: 
       if(_iter->second->IsAtFront()) 
        _iter->second->First(); 
       break; 
     } 
    } 

Answer 1

其他的東西都應該摺疊成一個開關，以使相關的步驟更接近;例如

case DIR_FORWARD_LOOPING: 
    _iter->second->Next(); 
    if (_iter->second->IsAtEnd()) { 
     _iter->second->First(); 
    } 
    break; 

......都在這一個案例中。重複一些函數調用並不是什麼大問題，因爲它會使整個操作順序更加清晰。

Answer 2

推入任何_iter->second是邏輯，沿着這些路線（假設你已經顯示的方法存在）：

class WhateverItIs 
{ 
public: 
    void Start() { if (m_forward) First(); else Last(); } 
    void Stop() { if (m_forward) Last(); else First(); } 
    void Advance() 
    { 
     if (m_forward) 
     Next(); 
     else 
     Previous(); 
     if (IsLast()) 
     { 
     if (m_loop) 
      Start(); 
     else 
      Stop(); 
     } 
    } 

private: 
    bool IsLast() const 
    { 
     return m_forward ? IsAtEnd() : IsAtFront(); 
    } 
    // Direction and looping are independent concepts.  
    bool m_forward; 
    bool m_loop; 
}; 

然後，你可以寫：

AnimMapIter _iter; 
_iter = _animations->find(name); 
if(_iter == _animations->end()) return; 

if(_curName != name) { 
    _curName = name; 
    _iter->second->Start(); 
} else { 
    _iter->second->Advance(); 
} 

---

編輯：使用自由函數和保持常量的示例。

void Start(Strip* s, bool forward) 
     { if (forward) s->First(); else s->Last(); } 
    void Stop(Strip* s, bool forward) 
     { if (forward) s->Last() else s->First(); } 
    void Advance(Strip* s, bool forward, bool loop) 
    { 
     if (forward) 
     s->Next(); 
     else 
     s->Previous(); 
     if (IsLast(s, forward)) 
     { 
     if (loop) 
      Start(s); 
     else 
      Stop(s); 
     } 
    } 

    bool IsLast(const Strip* s, bool forward) const 
    { 
     return forward ? s->IsAtEnd() : s->IsAtFront(); 
    } 

    bool Projector::IsForward() const 
    { 
     return dir == DIR_FORWARD_LOOPING || dir == DIR_FORWARD_NONLOOPING; 
    } 

    bool Projector::IsLooping() const 
    { 
     return dir == DIR_REVERSE_LOOPING || dir == DIR_FORWARD_LOOPING; 
    } 

    if(_curName != name) { 
     _curName = name; 
     Start(_iter->second, IsForward()); 
    } else { 
     Advance(_iter->second, IsForward(), IsLooping()); 
    }