template <class T, class Compare = std::equal_to<T>, bool = std::is_copy_constructible<T>::value>class HangingGetHelper
TODO(https://fxbug.dev/42124377): convert to generic fuchsia lib
template <class T, class Compare = std::equal_to<T>, bool = std::is_copy_constructible<T>::value>TODO(https://fxbug.dev/42124377): convert to generic fuchsia lib