C++ template operator not found as match
I'm trying to create a general operator<< for std::ostream and any Iterable type.
This is the code:
template <class T,template<class> class Iterable> inline std::ostream& operator<<(std::ostream& s,const Iterable<T>& iter){
s << "[ ";
bool first=false;
for(T& e : iter){
if(first){
first=false;
s << e;
}else{
s << ", " << e;
}
}
s << " ]";
return s;
}
Unfortunately my operator is not found as a match for a vector<uint> and the compiler tries to match with operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x) .
Any idea how I can change the overload to be recognized?
The direct solution to your problem is that vector is a template on two types, not one, so you'd want to write:
template <typename... T, template <typename... > class Iterable>
inline std::ostream& operator<<(std::ostream& os, const Iterable<T...>& iter)
{
s << "[ ";
bool first = true; // not false
for (const auto& e : iter) {
// rest as before
}
return s << " ]";
}
That works, but is a little unsatisfying - since some things that are templates aren't iterable and some things that aren't templates are. Furthermore, we do not actually need either Iterable or T in our solution. So how about we write something that takes any Range - where we define Range as something that has a begin() and end() :
template <typename Range>
auto operator<<(std::ostream& s, const Range& range)
-> decltype(void(range.begin()), void(range.end()), s)
{
// as above, except our container is now named 'range'
}
If that's too general, then you can do:
template <typename T> struct is_range : std::false_type;
template <typename T, typename A>
struct is_range<std::vector<T,A>> : std::true_type;
// etc.
template <typename Range>
typename std::enable_if<
is_range<Range>::value,
std::ostream&
>::type
operator<<(std::ostream& s, const Range& range)
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