get_if.h

Go to the documentation of this file.

#pragma once
 
#include "di/meta/algorithm.h"
#include "di/meta/language.h"
#include "di/util/get.h"
#include "di/vocab/optional/prelude.h"
#include "di/vocab/variant/variant_like.h"
#include "di/vocab/variant/variant_types.h"
#include "di/vocab/variant/variant_value.h"
 
namespace di::vocab {
template<size_t index, concepts::VariantLike Var, typename Res = meta::VariantValue<Var, index>>
constexpr auto get_if(Var&& variant) -> Optional<meta::RemoveRValueReference<Res>> {
    if (variant_index(variant) != index) {
        return nullopt;
    }
    return util::get<index>(util::forward<Var>(variant));
}
 
template<typename T, concepts::VariantLike Var, typename List = meta::VariantTypes<Var>,
         auto index = meta::Lookup<T, List>, typename Res = meta::VariantValue<Var, index>>
requires(meta::UniqueType<T, List>)
constexpr auto get_if(Var&& variant) -> Optional<meta::RemoveRValueReference<Res>> {
    if (variant_index(variant) != index) {
        return nullopt;
    }
    return util::get<index>(util::forward<Var>(variant));
}
}
 
namespace di {
using vocab::get_if;
}