sclass CollapsibleLeftPanel > MetaWithChangeListeners is Swingable {
  S sidePanelName;
  JComponent sideComponent, mainComponent;
  JSplitPane splitPane;
  settableWithVar bool expanded;
  SingleComponentPanel scp = singleComponentPanel();
  
  *(bool *expanded, S *sidePanelName, JComponent *sideComponent, JComponent *mainComponent) {
    splitPane = jhsplit(0.25, wrappedSideComponent(), null);
    varExpanded().onChangeAndNow(r updateScp);
  }
  
  void expand { setExpanded(true); }
  void collapse { setExpanded(false); }
  
  void updateScp {
    if (expanded) {
      splitPane.setRightComponent(mainComponent);
      scp.set(splitPane);
    } else
      scp.set(westAndCenterWithMargin(
        vstack(expandButton()), mainComponent));
  }
  
  JComponent expandButton() {
    ret jClickableImage_instantToolTip(#1103075, "Expand " + sidePanelName, r expand);
  }
  
  JComponent collapseButton() {
    ret jClickableImage_instantToolTip(#1103076, "Collapse " + sidePanelName, r collapse);
  }
  
  JComponent wrappedSideComponent() {
    //ret jSection(sidePanelName, sideComponent);
    ret northAndCenterWithMargin(
      westAndCenterWithMargin(collapseButton(), jlabel(sidePanelName)),
      sideComponent
    );
  }
  
  visual scp;
}