Boost.Hana: boost::hana::embedding< bool > Struct Template Reference

| Boost.Hana 1.4.0 Your standard library for metaprogramming |

boost::hana::embedding< bool > Struct Template Reference
Core

## Description

### template<bool = true>
struct boost::hana::embedding< bool >

Marks a conversion between data types as being an embedding.

To mark a conversion between two data types `To` and `From` as an embedding, simply use `embedding<true>` (or simply `embedding<>`) as a base class of the corresponding `to_impl` specialization. If a `to_impl` specialization does not inherit `embedding<true>` or `embedding<>`, then it is not considered an embedding by the `is_embedded` metafunction.

> #### Tip

> The boolean template parameter is useful for marking a conversion as an embedding only when some condition is satisfied.

## Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
#include <boost/hana/assert.hpp>
#include <boost/hana/core/to.hpp>
#include <boost/hana/core/when.hpp>
#include <vector>
namespace hana = boost::hana;
namespace boost { namespace hana {
template <typename To, typename From>
struct to_impl<std::vector<To>, std::vector<From>,
when<is_convertible<From, To>::value>>
: embedding<is_embedded<From, To>::value>
{
static std::vector<To> apply(std::vector<From> const& xs) {
std::vector<To> result;
for (auto const& x: xs)
result.push_back(to<To>(x));
return result;
}
};
}}
int main() {
BOOST_HANA_RUNTIME_CHECK(
hana::to<std::vector<int>>(std::vector<float>{1.1, 2.2, 3.3})
==
std::vector<int>{1, 2, 3}
);
static_assert(!hana::is_embedded<std::vector<float>, std::vector<int>>{}, "");
}