message: Replaced std::enable_if_t (>=C++14) with std::enable_if (>=C++11).
diff: @@ -72,8 +72,9 @@ class tstring {
  tstring(const char* str) : str_(str) {}
  - template <typename T, typename = std::enable_if_t<
  - std::is_same<T, absl::string_view>::value, T>>
  + template <typename T,
  + typename std::enable_if<std::is_same<T, absl::string_view>::value,
  + T>::type* = nullptr>
  explicit tstring(const T& str) : str_(str.data(), str.size()) {}
  tstring(tstring&&) noexcept = default;
  @@ -88,8 +89,9 @@ class tstring {
  return *this;
  }
  - template <typename T, typename = std::enable_if_t<
  - std::is_same<T, absl::string_view>::value, T>>
  + template <typename T,
  + typename std::enable_if<std::is_same<T, absl::string_view>::value,
  + T>::type* = nullptr>
  tstring& operator=(const T& str) {
  str_.assign(str.data(), str.size());
  @@ -118,8 +120,9 @@ class tstring {
  operator std::string() const { return str_; }
  - template <typename T, typename = std::enable_if_t<
  - std::is_same<T, absl::string_view>::value, T>>
  + template <typename T,
  + typename std::enable_if<std::is_same<T, absl::string_view>::value,
  + T>::type* = nullptr>
  operator T() const {
  return T(str_.data(), str_.size());
  }
  