如何移动 - 构建C ++ STL映射？

Question

以下代码在GCC 4.9.3下引发错误。

import java.awt.*;
import java.awt.event.*;
import java.beans.PropertyChangeEvent;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.plaf.*;
import javax.swing.plaf.basic.BasicSliderUI;
// import javax.swing.plaf.metal.MetalSliderUI;
// import javax.swing.plaf.synth.SynthSliderUI;
// import com.sun.java.swing.plaf.windows.WindowsSliderUI;

public class DragLimitedSliderTest {
  private static int MAXI = 80;
  private JComponent makeUI() {
    JSlider slider1 = makeSlider();
    JSlider slider2 = makeSlider();
    slider2.setUI(new BasicSliderUI(slider2) {
    //slider2.setUI(new WindowsSliderUI(slider2) {
    //slider2.setUI(new MetalSliderUI() {
    //slider2.setUI(new SynthSliderUI(slider2) {
      @Override protected TrackListener createTrackListener(JSlider slider) {
        return new TrackListener() {
          @Override public void mouseDragged(MouseEvent e) {
            //case HORIZONTAL:
            int halfThumbWidth = thumbRect.width / 2;
            int thumbLeft = e.getX() - offset;
            int maxPos = xPositionForValue(MAXI) - halfThumbWidth;
            if (thumbLeft > maxPos) {
              int x = maxPos + offset;
              MouseEvent me = new MouseEvent(
                e.getComponent(), e.getID(), e.getWhen(), e.getModifiers(),
                x, e.getY(),
                e.getXOnScreen(), e.getYOnScreen(),
                e.getClickCount(), e.isPopupTrigger(), e.getButton());
              e.consume();
              super.mouseDragged(me);
            } else {
              super.mouseDragged(e);
            }
          }
        };
      }
    });
    JSlider slider3 = makeSlider();

    JPanel p = new JPanel(new GridLayout(3, 1));
    p.add(slider1);
    p.add(slider2);
    p.add(new JLayer<JSlider>(slider3, new DisableInputLayerUI()));
    return p;
  }
  private static JSlider makeSlider() {
    JSlider slider = new JSlider(0, 100, 40) {
      @Override public void setValue(int n) {
        super.setValue(n);
      }
    };
    slider.setMajorTickSpacing(10);
    slider.setPaintTicks(true);
    slider.setPaintLabels(true);
    Dictionary dictionary = slider.getLabelTable();
    if (dictionary != null) {
      Enumeration elements = dictionary.elements();
      while (elements.hasMoreElements()) {
        JLabel label = (JLabel) elements.nextElement();
        int v = Integer.parseInt(label.getText());
        if (v > MAXI) {
          label.setForeground(Color.RED);
        }
      }
    }
    slider.getModel().addChangeListener(new ChangeListener() {
      @Override public void stateChanged(ChangeEvent e) {
        BoundedRangeModel m = (BoundedRangeModel) e.getSource();
        if (m.getValue() > MAXI) {
          m.setValue(MAXI);
        }
      }
    });
    return slider;
  }
  public static void main(String... args) {
    EventQueue.invokeLater(() -> {
      try {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
//         for (UIManager.LookAndFeelInfo laf: UIManager.getInstalledLookAndFeels()) {
//           if ("Nimbus".equals(laf.getName())) {
//             UIManager.setLookAndFeel(laf.getClassName());
//           }
//         }
      } catch (Exception e) {
        e.printStackTrace();
      }
      JFrame f = new JFrame();
      f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      f.getContentPane().add(new DragLimitedSliderTest().makeUI());
      f.setSize(320, 240);
      f.setLocationRelativeTo(null);
      f.setVisible(true);
    });
  }
}

class DisableInputLayerUI extends LayerUI<JSlider> {
  @Override public void installUI(JComponent c) {
    super.installUI(c);
    if (c instanceof JLayer) {
      JLayer jlayer = (JLayer) c;
      jlayer.setLayerEventMask(
        AWTEvent.MOUSE_EVENT_MASK |
        AWTEvent.MOUSE_MOTION_EVENT_MASK);
    }
  }
  @Override public void uninstallUI(JComponent c) {
    if (c instanceof JLayer) {
      JLayer jlayer = (JLayer) c;
      jlayer.setLayerEventMask(0);
    }
    super.uninstallUI(c);
  }
  private Rectangle thumbRect = new Rectangle(11, 19); //magic number
  private Rectangle focusRect = new Rectangle();
  private Rectangle contentRect = new Rectangle();
  private Rectangle trackRect = new Rectangle();
  private int offset;

  protected int xPositionForValue(JSlider slider, int value) {
    int min = slider.getMinimum();
    int max = slider.getMaximum();
    int trackLength = trackRect.width;
    double valueRange = (double) max - (double) min;
    double pixelsPerValue = (double) trackLength / valueRange;
    int trackLeft = trackRect.x;
    int trackRight = trackRect.x + (trackRect.width - 1);
    int xPosition;

    xPosition = trackLeft;
    xPosition += Math.round(pixelsPerValue * ((double) value - min));

    xPosition = Math.max(trackLeft, xPosition);
    xPosition = Math.min(trackRight, xPosition);

    return xPosition;
  }
  protected int getHeightOfTallestLabel(JSlider slider) {
    Dictionary dictionary = slider.getLabelTable();
    int tallest = 0;
    if (dictionary != null) {
      Enumeration keys = dictionary.keys();
      while (keys.hasMoreElements()) {
        JComponent label = (JComponent) dictionary.get(keys.nextElement());
        tallest = Math.max(label.getPreferredSize().height, tallest);
      }
    }
    return tallest;
  }
  @Override protected void processMouseEvent(MouseEvent e, JLayer<? extends JSlider> l) {
    JSlider slider = l.getView();
    if (e.getID() == MouseEvent.MOUSE_PRESSED) {
      //case HORIZONTAL:

      //recalculateIfInsetsChanged()
      Insets insetCache = slider.getInsets();
      Insets focusInsets = UIManager.getInsets("Slider.focusInsets");
      if (focusInsets == null) {
        focusInsets = new Insets(2, 2, 2, 2); //magic number
      }

      //calculateFocusRect()
      focusRect.x = insetCache.left;
      focusRect.y = insetCache.top;
      focusRect.width = slider.getWidth() - (insetCache.left + insetCache.right);
      focusRect.height = slider.getHeight() - (insetCache.top + insetCache.bottom);

      //calculateContentRect()
      contentRect.x = focusRect.x + focusInsets.left;
      contentRect.y = focusRect.y + focusInsets.top;
      contentRect.width = focusRect.width - (focusInsets.left + focusInsets.right);
      contentRect.height = focusRect.height - (focusInsets.top + focusInsets.bottom);

      //calculateThumbSize()
      Icon ti = UIManager.getIcon("Slider.horizontalThumbIcon");
      if (ti != null) {
        thumbRect.width = ti.getIconWidth();
        thumbRect.height = ti.getIconHeight();
      }

      //calculateTrackBuffer()
      int trackBuffer = 9; //magic number, Windows: 9, Metal: 10 ...

      //calculateTrackRect()
      int centerSpacing = thumbRect.height;
      if (slider.getPaintTicks())  centerSpacing += 8; //magic number getTickLength();
      if (slider.getPaintLabels()) centerSpacing += getHeightOfTallestLabel(slider);
      trackRect.x = contentRect.x + trackBuffer;
      trackRect.y = contentRect.y + (contentRect.height - centerSpacing - 1) / 2;
      trackRect.width = contentRect.width - (trackBuffer * 2);
      trackRect.height = thumbRect.height;

      //calculateThumbLocation()
      int valuePosition = xPositionForValue(slider, slider.getValue());
      thumbRect.x = valuePosition - (thumbRect.width / 2);
      thumbRect.y = trackRect.y;
      offset = e.getX() - thumbRect.x;
    }
  }
  @Override protected void processMouseMotionEvent(MouseEvent e, JLayer<? extends JSlider> l) {
    if (e.getID() == MouseEvent.MOUSE_DRAGGED) {
      JSlider slider = l.getView();
      //case HORIZONTAL:
      int halfThumbWidth = thumbRect.width / 2;
      int thumbLeft = e.getX() - offset;
      int maxPos = xPositionForValue(slider, 80) - halfThumbWidth;
      if (thumbLeft > maxPos) {
        e.consume();
        SliderUI ui = slider.getUI();
        if (ui instanceof BasicSliderUI) {
          ((BasicSliderUI) ui).setThumbLocation(maxPos, thumbRect.y);
        }
        slider.getModel().setValue(80);
      }
    }
  }
}

潜在错误是 #include <map> using namespace std; struct Movable { Movable(const Movable&) = delete; Movable(Movable&&) = default; }; class Foo { const map<int, Movable> m; Foo(map<int, Movable>&& _m) : m{_m} {} }; - 但AFAICS不应该尝试复制基础Movable。

Answer 1

由于_m有一个名称，使用时它是一个左值，你必须使用std::move：

class Foo {
    const map<int, Movable> m;
    Foo(map<int, Movable>&& _m) : m{std::move(_m)} {}
};