When I use map<string, string> kv; in protobuf 3.8.0, the next code works:
std::string_view key("key");
kv[key] = "value";
While in protobuf 3.19.4, the above code doesn't work.
The error msg is:
error: no match for 'operator[]' (operand types are 'google::protobuf::Map<std::__cxx11::basic_string , std::__cxx11::basic_string>' and 'std::string_view' {aka 'std::basic_string_view'})
In 3.8.0, Map::operator[] is declared as:
Value& operator[](const Key& k)
Where, in your case, Key is std::string. std::string_view is convertible to std::string, which is why the code works in 3.8.0.
In 3.19.4, Map::operator[] is declared as:
template <typename K = key_type>
T& operator[](const key_arg<K>& key)
template <
typename K = key_type,
// Disable for integral types to reduce code bloat.
typename = typename std::enable_if<!std::is_integral<K>::value>::type>
T& operator[](key_arg<K>&& key)
Where key_arg is declared as:
template <typename LookupKey>
using key_arg = typename internal::TransparentSupport<key_type>::template key_arg<LookupKey>;
And, in your case, key_type is std::string. std::string_view is not convertible to TransparentSupport::key_arg, which is why the code doesn't work in 3.19.4.