C++ Unreadable Template Example

/**
 *  Attempts to perform an operation while holding
 *  the lock, but only if the lock may be acquired
 *  without blocking.
 *
 *  \tparam T
 *      The type of the functor that is
 *      to be executed while the lock is
 *      held.
 *  \tparam Args
 *      The types of a parameter pack to be
 *      forwarded to operator () of the
 *      instance of \em T supplied.
 *
 *  \param [in] exec
 *      The functor to execute while the
 *      lock is held.
 *  \param [in] args
 *      A parameter pack whose types are
 *      given by \em Args which shall be
 *      forwarded to operator () of
 *      \em exec.
 *  \param [out] result
 *      A pointer to an object of the type
 *      returned by operator () of
 *      \em exec.  This address location
 *      will be populated with the value
 *      returned by \em exec with arguments
 *      \em args.  May be \em nullptr if
 *      the return value of \em exec is
 *      not desired.
 *
 *  \return
 *      \em true if the lock was acquired
 *      and \em exec was called, \em false
 *      otherwise.
 */
template <typename T, typename... Args>
auto TryExecute (
    const T & exec,
    Args &&... args,
    decltype(exec(std::forward<Args>(args)...)) * result
) -> typename std::enable_if<
    !std::is_same<
        decltype(exec(std::forward<Args>(args)...)),
        void
    >::value,
    bool
>::type {

    if (!TryAcquire()) return false;

    try {

        if (result==nullptr) exec(std::forward<Args>(args)...);
        else *result=exec(std::forward<Args>(args)...);

    } catch (...) {

        Release();

        throw;

    }

    Release();

    return true;

}