92 lines
2.5 KiB
C++
92 lines
2.5 KiB
C++
/** @file cond.hpp
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*
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* author: Roland Conybeare
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**/
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#pragma once
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#include "ppdetail_atomic.hpp"
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#include <iostream>
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#include <type_traits>
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namespace xo {
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/** @class cond_impl
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* @brief conditional stream inserter implementation
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*
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* @tparam T type printed when condition is true
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* @tparam U type printed when condition is false
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**/
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template <typename T, typename U>
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struct cond_impl {
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public:
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cond_impl(bool condition, T const & then_value, U const & else_value)
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: condition_{condition},
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then_value_{then_value},
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else_value_{else_value} {}
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bool condition() const { return condition_; }
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T const & then_value() const { return then_value_; }
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U const & else_value() const { return else_value_; }
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private:
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bool condition_;
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T then_value_;
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U else_value_;
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};
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/** Create conditional stream inserter.
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*
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* @param condition when true, print @p then_value; otherwise print @p else_value
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* @param then_value value to print when condition is true
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* @param else_value value to print when condition is false
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*
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* Example:
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* @code
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* std::cout << cond(ptr != nullptr, xtag("ptr", *ptr), "nullptr");
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* @endcode
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**/
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template <typename T, typename U>
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auto
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cond(bool condition, T && then_value, U && else_value)
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{
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return cond_impl<std::decay_t<T>, std::decay_t<U>>
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(condition,
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std::forward<T>(then_value),
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std::forward<U>(else_value));
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}
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/** Stream insertion operator for cond_impl **/
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template <typename T, typename U>
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inline std::ostream &
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operator<<(std::ostream & os, cond_impl<T, U> const & c)
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{
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if (c.condition())
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os << c.then_value();
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else
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os << c.else_value();
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return os;
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}
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#ifndef ppdetail_atomic
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namespace print {
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/** Pretty-printing support for cond_impl **/
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template <typename T, typename U>
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struct ppdetail<cond_impl<T, U>> {
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using target_type = cond_impl<T, U>;
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static bool print_pretty(const ppindentinfo & ppii,
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const target_type & c)
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{
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if (c.condition())
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return ppdetail<T>::print_pretty(ppii, c.then_value());
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else
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return ppdetail<U>::print_pretty(ppii, c.else_value());
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}
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};
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}
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#endif
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}
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/* end cond.hpp */
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