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Add ReplacePlaceholders #451

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Dec 22, 2021
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Add ReplacePlaceholders #451

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20 changes: 20 additions & 0 deletions include/llama/Meta.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -65,5 +65,25 @@ namespace llama

template<typename FromList, template<auto...> class ToList>
using mp_unwrap_values_into = typename mp_unwrap_values_into_impl<FromList, ToList>::type;

template<typename E, typename... Args>
struct ReplacePlaceholdersImpl
{
using type = E;
};
template<std::size_t I, typename... Args>
struct ReplacePlaceholdersImpl<boost::mp11::mp_arg<I>, Args...>
{
using type = boost::mp11::mp_at_c<boost::mp11::mp_list<Args...>, I>;
};

template<template<typename...> typename E, typename... Ts, typename... Args>
struct ReplacePlaceholdersImpl<E<Ts...>, Args...>
{
using type = E<typename ReplacePlaceholdersImpl<Ts, Args...>::type...>;
};
} // namespace internal

template<typename Expression, typename... Args>
using ReplacePlaceholders = typename internal::ReplacePlaceholdersImpl<Expression, Args...>::type;
} // namespace llama
27 changes: 27 additions & 0 deletions tests/meta.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
#include "common.hpp"

TEST_CASE("ReplacePlaceholders")
{
using namespace boost::mp11;
using namespace tag;

STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<int, A, B, C>, int>);
STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<std::string, A, B, C>, std::string>);
STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<Particle, A, B, C>, Particle>);

STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<_1, A, B, C>, A>);
STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<_2, A, B, C>, B>);
STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<_3, A, B, C>, C>);

STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<mp_list<_1>, A, B, C>, mp_list<A>>);
STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<mp_list<_1, _2>, A, B, C>, mp_list<A, B>>);
STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<mp_list<_3, _1, _2>, A, B, C>, mp_list<C, A, B>>);

STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<mp_list<_3, _1, _1>, A, B, C>, mp_list<C, A, A>>);
STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<mp_list<_2, _2, _2>, A, B, C>, mp_list<B, B, B>>);

STATIC_REQUIRE(std::is_same_v<llama::ReplacePlaceholders<mp_list<mp_list<_2>>, A, B, C>, mp_list<mp_list<B>>>);
STATIC_REQUIRE(std::is_same_v<
llama::ReplacePlaceholders<mp_list<mp_list<_2, _1>, _2, mp_list<_2, mp_list<_3>>>, A, B, C>,
mp_list<mp_list<B, A>, B, mp_list<B, mp_list<C>>>>);
}