Do The Simplest Thing That Could Possibly Work

今天加 SphereStack test，果然爛掉。為什麼？這是因為個人奉行：

Do the simplest thing that could possibly work.

這就是 test-driven 的精神，除非測試失敗，否則不要寫多餘的程式碼，即使下個測試會用到。因此原先系統不支援圓形物體，這就是為什麼會爛掉的原因。

在這當下，才是真正寫程式碼的時機。

  if (config.shape_config->type == ShapeConfig::Polygon) {
    ...
    b2PolygonShape shape_impl;
    ...

    b2FixtureDef config_impl;
    config_impl.shape = &shape_impl;
    config_impl.friction = config.friction;
    config_impl.restitution = config.restitution;
    config_impl.density = config.density;

    itself_->CreateFixture(&config_impl);
  }
  else if (config.shape_config->type == ShapeConfig::Circle) {
    ...
    b2CircleShape shape_impl;
    ...

    b2FixtureDef config_impl;
    config_impl.shape = &shape_impl;
    config_impl.friction = config.friction;
    config_impl.restitution = config.restitution;
    config_impl.density = config.density;

    itself_->CreateFixture(&config_impl);  
  }

好多重複的程式碼，雖然可以立即 refactor，改善既有的程式碼，但目前測試都沒過，千萬別急著動，這也是 test-driven 的精神。測試過了再來 refactor，順便確保 refactored code 是對的。

跑測試，沒過。見鬼了！不是的，因為我又少支援線段物體，只好再加上去讓他過。

  if (config.shape_config->type == ShapeConfig::Polygon) { 
    ... 
  }
  else if (config.shape_config->type == ShapeConfig::Circle) {
    ...
  }
  else if (config.shape_config->type == ShapeConfig::Edge) {
    ...
    b2EdgeShape shape_impl;
    ...

    b2FixtureDef config_impl;
    config_impl.shape = &shape_impl;
    config_impl.friction = config.friction;
    config_impl.restitution = config.restitution;
    config_impl.density = config.density;

    itself_->CreateFixture(&config_impl);  
  }

更多重複的程式碼。這不重要，重要的是先跑測試。啊！過了。接著再來 refactor 吧！

  b2Shape* shape_wrapper;

  if (config.shape_config->type == ShapeConfig::Polygon) {
    ...
    b2PolygonShape* shape_impl = new b2PolygonShape();
    shape_wrapper = shape_impl;
    ...
  }
  else if (config.shape_config->type == ShapeConfig::Circle) {
    ...
    b2CircleShape* shape_impl = new b2CircleShape();
    shape_wrapper = shape_impl;
    ...
  }
  else if (config.shape_config->type == ShapeConfig::Edge) {
    ...
    b2EdgeShape* shape_impl = new b2EdgeShape();
    shape_wrapper = shape_impl;
    ...
  }
  else {
    return;
  }

  b2FixtureDef config_impl;
  config_impl.shape = shape_wrapper;
  config_impl.friction = config.friction;
  config_impl.restitution = config.restitution;
  config_impl.density = config.density;

  itself_->CreateFixture(&config_impl);

  delete shape_wrapper;

再跑測試，還是過，refactor 品質沒有問題 (可能 code 還很髒，可能還有 bug，不過至少可以過 SphereStack)。Do the simplest thing that could possibly work.