C++中灵活的枚举

Question

我如何组织枚举,以便每个枚举条目都有参数,例如我在Haxe中可以做的,例如:

enum GraphicAct {
  ClearScreen; 
  MoveTo(x:Float, y:Float);
  LineTo(x:Float, y:Float);
  FillColor(color:Int);
  EndFill;
}

function main(){
  var actions:Array<GraphicAct>;
  actions.push(ClearScreen);
  actions.push(FillColor(0xaaffff));
  actions.push(MoveTo(100, 100));
  actions.push(LineTo(200, 100));
  actions.push(LineTo(100, 200));
  actions.push(EndFill);


  for(act in actions){
    switch(act){
       case ClearScreen: // do clear screen here...
       case MoveTo(x, y): // move position
       case LineTo(x, y): // move position
    }
  }
}

据我所知,C++仅支持没有参数的枚举条目,如"ClearScreen"和"EndFill",但在这种情况下,我如何在C++中组织命令序列,就像我在图形命令中的例子一样？

Answer 1

你可以用union和enum,是这样的:

enum class EGraphicActType
{
    ClearScreen, MoveTo, LineTo, FillColorData, EnfFillData
};

struct ClearScreenData {};
struct MoveToData { float x; float y;};
struct LineToData { float x; float y;};
struct FillColorData { Int color;};
struct EnfFillData {};

struct GraphicAct {
    EGraphicActType type;
    union
    {
        ClearScreenData clearScreenData;
        MoveToData moveToData;
        LineToData lineToData;
        FillColorData fillColorData;
        EnfFillData endFillData;
    } data;
};

如果你有权使用提升,你可以使用boost::variant.