Qt：枚举值做函数参数

enum做函数参数报错：ISO C++ forbids forward references to 'enum' types

https://blog.csdn.net/weixin_45360983/article/details/100125041

改成：

imagewidget.h

enum class BorderType;
enum class BorderType
{
    TOP_BORDER,
    BOTTOM_BORDER,
    LEFT_BORDER,
    RIGHT_BORDER
};

void deleteBlackBorder(BorderType border_type);

imagewidget.cpp 

void ImageWidget::deleteBlackBorder(BorderType border_type)
{
    switch (border_type) {
    case BorderType::TOP_BORDER:
        break;
    case BorderType::BOTTOM_BORDER:
        break;
    case BorderType::LEFT_BORDER:
        break;
    case BorderType::RIGHT_BORDER:
        break;
    }
}