// Matrix Construct // // Copyright (C) Matrix Construct Developers, Authors & Contributors // Copyright (C) 2016-2019 Jason Volk <jason@zemos.net> // // Permission to use, copy, modify, and/or distribute this software for any // purpose with or without fee is hereby granted, provided that the above // copyright notice and this permission notice is present in all copies. The // full license for this software is available in the LICENSE file. #pragma once #define HAVE_IRCD_M_QUERY_H namespace ircd::m { template<class R> R query(std::nothrow_t, const event::idx &, const string_view &key, R&& def, const std::function<R (const string_view &)> &); template<class F> auto query(std::nothrow_t, const event::idx &, const string_view &key, F&&); template<class R, class F> R query(const event::idx &, const string_view &key, R&& def, F&&); template<class F> auto query(const event::idx &, const string_view &key, F&&); } /// Like m::get(), but the closure returns a value which will then be returned /// by these functions. This elides the pattern of returning a result through /// the lambda capture when one simply wants to condition on the fetched value /// rather than make further use of it. /// template<class F> auto ircd::m::query(const event::idx &event_idx, const string_view &key, F&& closure) { using R = typename std::invoke_result<F, const string_view &>::type; R ret; m::get(event_idx, key, [&ret, &closure] (const string_view &value) { ret = closure(value); }); return ret; } template<class R, class F> R ircd::m::query(const event::idx &event_idx, const string_view &key, R&& r, F&& f) { return query(std::nothrow, event_idx, key, std::forward<R>(r), std::forward<F>(f)); } /// See other overload documentation first. This overload implements /// non-throwing behavior when the event_idx/key(column) is not found by /// calling the closure with a default-constructed string so the closure can /// return a default value. /// template<class F> auto ircd::m::query(std::nothrow_t, const event::idx &event_idx, const string_view &key, F&& closure) { using R = typename std::invoke_result<F, const string_view &>::type; R ret; const auto assign { [&ret, &closure](const string_view &value) { ret = closure(value); } }; if(unlikely(!m::get(std::nothrow, event_idx, key, assign))) assign(string_view{}); return ret; } /// See other overload documentation first. This overload implements /// non-throwing behavior when the event_idx/key(column) is not found by /// returning a default value supplied by the caller. /// template<class R> R ircd::m::query(std::nothrow_t, const event::idx &event_idx, const string_view &key, R&& default_, const std::function<R (const string_view &)> &closure) { R ret{std::forward<R>(default_)}; m::get(std::nothrow, event_idx, key, [&ret, &closure] (const string_view &value) { ret = closure(value); }); return ret; }