const作为模板参数 [英] const-ness as template argument
本文介绍了const作为模板参数的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我有两个结构:
// ----- non-const -----
struct arg_adapter
{
EArgType type; // fmtA, fmtB, ...
union
{
TypeA * valueA;
TypeB * valueB;
// ... more types
}
arg_adapter(TypeA & value) : type(fmtA), valueA(&value) {}
arg_adapter(TypeB & value) : type(fmtB), valueB(&value) {}
// ...
}
// ----- const version -----
struct const_arg_adapter
{
EArgType type; // fmtA, fmtB, ...
union
{
TypeA const * valueA;
TypeB const * valueB;
// ... more types
}
arg_adapter(TypeA const & value) : type(fmtA), valueA(&value) {}
arg_adapter(TypeB const & value) : type(fmtB), valueB(&value) {}
// ...
}
它们应该在以下方法中使用:
They are supposed to be used in methods such as:
Convert(const_arg_adapter from, arg_adapter to)
有多个TypeX'(约5个, ,大多数是原始的。这是为了避免维护不同的原型。
There are multiple TypeX' (about 5, may become more), most of them primitive. This is to avoid maintaining different prototypes.
现在我的问题了 - )
有没有办法使常量是模板参数?
我的目标是保持只有一个结构,即
Is there a way to make the const-ness a template parameter? My goal is to maintain only one struct, i.e.
template <Qualifier CONSTNESS>
struct arg_adapter_t
{
...
CONSTNESS TypeA * valueA;
...
}
推荐答案
您可以接受元功能,并且可以应用
You can make it accept a metafunction and you can apply any transformation you like
template<template<typename> class F>
struct arg_adapter
{
EArgType type; // fmtA, fmtB, ...
union
{
typename F<TypeA>::type * valueA;
typename F<TypeB>::type * valueB;
// ... more types
};
arg_adapter(typename F<TypeA>::type & value) : type(fmtA), valueA(&value) {}
arg_adapter(typename F<TypeB>::type & value) : type(fmtB), valueB(&value) {}
// ...
};
typename arg_adapter<boost::add_const> const_adapter;
typename arg_adapter<boost::mpl::identity> nonconst_adapter;
或接受元功能类,以获得更大的灵活性(包括使 F
具有默认值您的 arg_adapter
等未知的参数。
Or accept a metafunction class to get more flexibility (including the ability to make F
have default arguments not known to your arg_adapter
and such.
template<typename F>
struct arg_adapter
{
EArgType type; // fmtA, fmtB, ...
union
{
typename apply<F, TypeA>::type * valueA;
typename apply<F, TypeB>::type * valueB;
// ... more types
};
arg_adapter(typename apply<F, TypeA>::type & value) : type(fmtA), valueA(&value) {}
arg_adapter(typename apply<F, TypeB>::type & value) : type(fmtB), valueB(&value) {}
// ...
};
typename arg_adapter< lambda< boost::add_const<_> >::type > const_adapter;
typename arg_adapter< lambda< boost::mpl::identity<_> >::type > nonconst_adapter;
这篇关于const作为模板参数的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文