mirror of https://github.com/tstack/lnav.git
107 lines
3.1 KiB
C++
107 lines
3.1 KiB
C++
/**
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* Copyright (c) 2019, Timothy Stack
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*
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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* * Neither the name of Timothy Stack nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ''AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef lnav_opt_util_hh
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#define lnav_opt_util_hh
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#include <stdlib.h>
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#include "intern_string.hh"
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#include "optional.hpp"
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namespace detail {
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template<class T>
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typename std::enable_if<std::is_void<T>::value, T>::type
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void_or_nullopt()
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{
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return;
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}
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template<class T>
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typename std::enable_if<not std::is_void<T>::value, T>::type
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void_or_nullopt()
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{
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return nonstd::nullopt;
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}
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template<class T>
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struct is_optional : std::false_type {
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};
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template<class T>
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struct is_optional<nonstd::optional<T>> : std::true_type {
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};
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} // namespace detail
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template<class T,
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class F,
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std::enable_if_t<detail::is_optional<std::decay_t<T>>::value, int> = 0>
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auto
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operator|(T&& t, F f)
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-> decltype(detail::void_or_nullopt<decltype(f(std::forward<T>(t).
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operator*()))>())
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{
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using return_type = decltype(f(std::forward<T>(t).operator*()));
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if (t)
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return f(std::forward<T>(t).operator*());
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else
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return detail::void_or_nullopt<return_type>();
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}
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template<class T>
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optional_constexpr nonstd::optional<typename std::decay<T>::type>
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make_optional_from_nullable(T&& v)
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{
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if (v != nullptr) {
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return nonstd::optional<typename std::decay<T>::type>(
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std::forward<T>(v));
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}
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return nonstd::nullopt;
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}
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template<template<typename, typename...> class C, typename T>
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nonstd::optional<T>
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cget(const C<T>& container, size_t index)
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{
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if (index < container.size()) {
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return container[index];
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}
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return nonstd::nullopt;
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}
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inline nonstd::optional<const char*>
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getenv_opt(const char* name)
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{
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return make_optional_from_nullable(getenv(name));
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}
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#endif
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