如何使用boost预处理器生成访问器？

Question

例如

class A
{
    int m_x;
    float m_y;
    double m_z;

    int x() const {return m_x;}
    float y() const {return m_y;}
    double z() const {return m_z;}
};

变得像

class A
{
    MY_MACRO((int)(float)(double), (x)(y)(z));
};

请使用boost预处理器序列来执行此操作,因为此宏将与已使用boost预处理器序列的其他现有宏组合.

Answer 1

免责声明:您应该等待,即使您对此答案感到满意,也会出现更好的答案,因为我不是专家,这可能不是最好的方法.

第一种方法:

//two different sequences
struct A
{
    MY_MACRO1((int)(float)(double),(x)(y)(z))
};

我认为这种方法给出了不那么可怕的宏:

#define DECLARE_DATA_MEMBER1(R,TYPES,INDEX,NAME) \
BOOST_PP_SEQ_ELEM(INDEX,TYPES) BOOST_PP_CAT(m_,NAME);

#define DEFINE_ACCESSOR1(R,TYPES,INDEX,NAME) \
BOOST_PP_SEQ_ELEM(INDEX,TYPES) NAME(){ return BOOST_PP_CAT(m_,NAME); }

#define MY_MACRO1(TYPES,NAMES) \
BOOST_PP_SEQ_FOR_EACH_I(DECLARE_DATA_MEMBER1,TYPES,NAMES) \
public: \
BOOST_PP_SEQ_FOR_EACH_I(DEFINE_ACCESSOR1,TYPES,NAMES)

MY_MACRO获得两个序列:TYPES和NAMES.为了声明数据成员,我使用宏BOOST_PP_SEQ_FOR_EACH_I在序列上使用a 并将序列作为数据.这个"调用" 有4个参数:未使用(我不知道它做了什么),(类型序列),(告诉我们现在在哪个迭代,从0开始),和(元素)与此迭代对应的原始序列). 该"机构"的和简单,我们只是得到了在类型序列个元素,并连接带.NAMESDECLARE_DATA_MEMBER1TYPESDECLARE_DATA_MEMBER1RTYPESINDEXNAMENAMES
DECLARE_DATA_MEMBER1DEFINE_ACCESSOR1INDEXm_NAME

第二种方法:

//just one sequence but you need to put two sets of parentheses around each pair
struct B
{
    MY_MACRO2(((int, x))((float,y))((double,z)))
};

这个仍然相当简单,但不方便使用双括号.

#define DECLARE_DATA_MEMBER2(R,_,TYPE_AND_NAME) \
BOOST_PP_TUPLE_ELEM(2,0,TYPE_AND_NAME) BOOST_PP_CAT(m_,BOOST_PP_TUPLE_ELEM(2,1,TYPE_AND_NAME));

#define DEFINE_ACCESSOR2(R,_,TYPE_AND_NAME) \
BOOST_PP_TUPLE_ELEM(2,0,TYPE_AND_NAME) BOOST_PP_TUPLE_ELEM(2,1,TYPE_AND_NAME)(){ return BOOST_PP_CAT(m_,BOOST_PP_TUPLE_ELEM(2,1,TYPE_AND_NAME)); }

#define MY_MACRO2(TYPES_AND_NAMES) \
BOOST_PP_SEQ_FOR_EACH(DECLARE_DATA_MEMBER2,_,TYPES_AND_NAMES) \
public: \
BOOST_PP_SEQ_FOR_EACH(DEFINE_ACCESSOR2,_,TYPES_AND_NAMES)

这次只有一个序列,所以我们不需要辅助宏中的索引.因此BOOST_PP_SEQ_FOR_EACH,使用宏在TYPES_AND_NAMES上使用DECLARE_DATA_MEMBER2,而不传递任何额外数据.这个宏接收三个"参数":R再次未使用,_(或者DATA,此处也未使用)和TYPE_AND_NAME(表单中的元组(TYPE,NAME)).
在两个辅助宏的"主体"中,BOOST_PP_TUPLE_ELEM用于获取类型(索引= 0)或名称(索引= 1).这个宏需要传递元组的大小,你想要的元素的索引和元组.

第三种方法:

//one sequence but the macro is more complex
struct C
{
    MY_MACRO3((int,x)(float,y)(double,z))
};

这个宏大量借用了BOOST_FUSION_ADAPT_STRUCT类似的宏.

//Heavily "inspired" from BOOST_FUSION_ADAPT_STRUCT
#define CREATE_MY_MACRO_PLACEHOLDER_FILLER_0(X, Y)  \
    ((X, Y)) CREATE_MY_MACRO_PLACEHOLDER_FILLER_1
#define CREATE_MY_MACRO_PLACEHOLDER_FILLER_1(X, Y)  \
    ((X, Y)) CREATE_MY_MACRO_PLACEHOLDER_FILLER_0
#define CREATE_MY_MACRO_PLACEHOLDER_FILLER_0_END
#define CREATE_MY_MACRO_PLACEHOLDER_FILLER_1_END

#define DECLARE_DATA_MEMBER3(R,_,TYPE_AND_NAME) \
BOOST_PP_TUPLE_ELEM(2,0,TYPE_AND_NAME) BOOST_PP_CAT(m_,BOOST_PP_TUPLE_ELEM(2,1,TYPE_AND_NAME));

#define DEFINE_ACCESSOR3(R,_,TYPE_AND_NAME) \
BOOST_PP_TUPLE_ELEM(2,0,TYPE_AND_NAME) BOOST_PP_TUPLE_ELEM(2,1,TYPE_AND_NAME)(){ return BOOST_PP_CAT(m_,BOOST_PP_TUPLE_ELEM(2,1,TYPE_AND_NAME)); }

#define MY_MACRO3(TYPES_AND_NAMES) \
BOOST_PP_SEQ_FOR_EACH(DECLARE_DATA_MEMBER3,_,BOOST_PP_CAT(CREATE_MY_MACRO_PLACEHOLDER_FILLER_0 TYPES_AND_NAMES,_END)) \
public: \
BOOST_PP_SEQ_FOR_EACH(DEFINE_ACCESSOR3,_,BOOST_PP_CAT(CREATE_MY_MACRO_PLACEHOLDER_FILLER_0 TYPES_AND_NAMES,_END))

在这种方法中,辅助宏基本上没有变化.唯一的(大)不同的是,在使用的for_each的顺序不是简单的TYPES_AND_NAMES,但BOOST_PP_CAT(CREATE_MY_MACRO_PLACEHOLDER_FILLER_0 TYPES_AND_NAMES,_END).这是强制双括号的巧妙技巧.它的工作原理如下:

CREATE_MY_MACRO_PLACEHOLDER_FILLER_0(int,x)(float,y)_END
    //CREATE_MY_MACRO_PLACEHOLDER_FILLER_0(A,B)->((A,B))CREATE_MY_MACRO_PLACEHOLDER_FILLER_1
((int,x))CREATE_MY_MACRO_PLACEHOLDER_FILLER_1(float,y)_END
    //CREATE_MY_MACRO_PLACEHOLDER_FILLER_1(A,B)->((A,B))CREATE_MY_MACRO_PLACEHOLDER_FILLER_0
((int,x))((float,y))CREATE_MY_MACRO_PLACEHOLDER_FILLER_0_END
    //CREATE_MY_MACRO_PLACEHOLDER_FILLER_0_END->
((int,x))((float,y))

在Coliru上奔跑.