I frequently encounter the usecase where I have to check whether a set of keys is contained in a set of nested maps. I currently have an implementation for a number of practical nesting depths that look something like this:
template< typename Key1T, typename Key2T, typename ValueT >
bool contains
( std::map< Key1T, std::map< Key2T, ValueT > > const & m
, Key1T const & k1
, Key2T const & k2
)
{
return m.contains( k1 ) && m.at( k1 ).contains( k2 );
}
I was wondering if there was a way to implement this as a single function for all possible nesting depths, maybe facilitating variadic templates?
>Solution :
I question the motives behind doing something like this, but here you go:
template<typename FirstKey, typename InnerMap, typename... RemainingKeys>
bool contains(std::map<FirstKey, InnerMap> const& m, FirstKey const& firstKey, RemainingKeys const&... remainingKeys) {
auto it = m.find(firstKey);
if constexpr (sizeof...(remainingKeys) == 0) {
return it != m.end();
} else {
return it != m.end() && contains(it->second, remainingKeys...);
}
}