假设我有一个元组,例如
using BaseTuple = std::tuple<int, double, string>;
,我想从给定的可变参数索引序列定义新类型,以及与 BaseTuple 相互转换的方法。例如,CustomTuple<0,1> 应派生自 tupleusing BaseTuple = tuple<int, double, string>;
template <size_t... I>
struct CustomTuple: public tuple<tuple_element_t<I, BaseTuple>...>{
using tuple<tuple_element_t<I, BaseTuple>...>::tuple;
static CustomTuple fromBaseTuple(const BaseTuple& key){
return {get<I>(key)...};
};
BaseTuple toBaseTuple(){
BaseTuple t;
((get<tuple_element_t<I, BaseTuple>>(t) = get<tuple_element_t<I, BaseTuple>>(t)), ...);
return t;
}
};
如果元组具有唯一类型,上面的代码就可以工作,但我想知道是否有任何方法可以处理重复类型。我找不到用它的索引迭代 I... 的方法。
大致如下:
template <std::size_t... S>
BaseTuple toBaseTuple(std::index_sequence<S...>) {
BaseTuple t;
((std::get<I>(t) = std::get<S>(*this)), ...);
return t;
}
BaseTuple toBaseTuple(){
return toBaseTuple(std::make_index_sequence<sizeof...(I)>{});
}