compose.h

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#ifndef GAUDIKERNEL_COMPOSE_H
#define GAUDIKERNEL_COMPOSE_H

namespace details
{

#if __cplusplus > 201402L

  // C++17 version: https://godbolt.org/g/2vAZQt
  template <typename... lambda_ts>
  struct composer_t : lambda_ts... {
    template <typename... T>
    composer_t( T&&... t ) : lambda_ts( std::forward<T>( t ) )...
    {
    }

    using lambda_ts::operator()...;
  };

#else

  template <typename... lambda_ts>
  struct composer_t;

  template <typename lambda_t>
  struct composer_t<lambda_t> : lambda_t {
    composer_t( const lambda_t& lambda ) : lambda_t{lambda} {}
    composer_t( lambda_t&& lambda ) : lambda_t{std::move( lambda )} {}

    using lambda_t::operator();
  };

  template <typename lambda_t, typename... more_lambda_ts>
  struct composer_t<lambda_t, more_lambda_ts...> : lambda_t, composer_t<more_lambda_ts...> {
    using super_t = composer_t<more_lambda_ts...>;

    template <typename... lambda_ts>
    composer_t( const lambda_t& lambda, lambda_ts&&... more_lambdas )
        : lambda_t{lambda}, super_t{std::forward<lambda_ts>( more_lambdas )...}
    {
    }
    template <typename... lambda_ts>
    composer_t( lambda_t&& lambda, lambda_ts&&... more_lambdas )
        : lambda_t{std::move( lambda )}, super_t{std::forward<lambda_ts>( more_lambdas )...}
    {
    }

    using lambda_t::operator();
    using super_t::operator();
  };
#endif
}

template <typename... lambda_ts>
details::composer_t<std::decay_t<lambda_ts>...> compose( lambda_ts&&... lambdas )
{
  return {std::forward<lambda_ts>( lambdas )...};
}
#endif