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