Loki库读解-扩展TypeList:Typelist生成器、MaxSizeOf

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Loki中的TYPELIST_**宏还是太难用了,因为无法支持不定参数。

借鉴于BOOST中的Tuple的想法,实现了这个Typelist_Maker:

template<class T1  = NullType, class T2  = NullType, class T3  = NullType, class T4  = NullType, class T5  = NullType,
         class T6  = NullType, class T7  = NullType, class T8  = NullType, class T9  = NullType, class T10 = NullType,
         class T11 = NullType, class T12 = NullType, class T13 = NullType, class T14 = NullType, class T15 = NullType,
         class T16 = NullType, class T17 = NullType, class T18 = NullType, class T19 = NullType, class T20 = NullType,
         class T21 = NullType, class T22 = NullType, class T23 = NullType, class T24 = NullType, class T25 = NullType,
         class T26 = NullType, class T27 = NullType, class T28 = NullType, class T29 = NullType, class T30 = NullType,
         class T31 = NullType, class T32 = NullType, class T33 = NullType, class T34 = NullType, class T35 = NullType,
         class T36 = NullType, class T37 = NullType, class T38 = NullType, class T39 = NullType, class T40 = NullType,
         class T41 = NullType, class T42 = NullType, class T43 = NullType, class T44 = NullType, class T45 = NullType,
         class T46 = NullType, class T47 = NullType, class T48 = NullType, class T49 = NullType, class T50 = NullType>
    struct Typelist_Maker
{
private:
    typedef TYPELIST_50(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10,
                        T11, T12, T13, T14, T15, T16, T17, T18, T19, T20,
                        T21, T22, T23, T24, T25, T26, T27, T28, T29, T30,
                        T31, T32, T33, T34, T35, T36, T37, T38, T39, T40,
                        T41, T42, T43, T44, T45, T46, T47, T48, T49, T50) TmpList;
public:                           
    typedef typename EraseAll<TmpList, NullType>::Result Result; 
};

这下,世界会清净多了。

然后一个小扩展是MaxSizeOf,取一组类型中的最大大小。

传统方法是使用union的,当然是感觉不爽了。

template<class Tlist>
    struct MaxSizeOf;

template<>
    struct MaxSizeOf<NullType>
{
    enum {value = 0}; 
};       

template<class Head, class Tail>
    struct MaxSizeOf<Typelist<Head, Tail> >
{
private:
    enum {MaxSizeOfTail = MaxSizeOf<Tail>::value};
public:   
    enum {value = (sizeof(Head) > MaxSizeOfTail ? sizeof(Head) : MaxSizeOfTail)}; 
};

 

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