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Used index_sequence to get rid of recursion in interpret_tuple.

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Wonderful stuff, shaped after code samples from cppreference and
stackoverflow.
This commit is contained in:
rbock 2014-05-06 22:41:19 +02:00
parent f57ba13955
commit b9133cf3a1
1 changed files with 25 additions and 32 deletions
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57
include/sqlpp11/vendor/interpret_tuple.h vendored
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@ -30,47 +30,40 @@
#include <tuple>
#include <sqlpp11/type_traits.h>
#include <sqlpp11/serialize.h>
#include <sqlpp11/detail/index_sequence.h>
namespace sqlpp
{
template<typename Context, typename Tuple>
struct tuple_interpreter_t
template<typename Element, typename Separator, typename Context>
static void interpret_tuple_element(const Element& element, const Separator& separator, Context& context, size_t index)
{
template<typename Separator>
static void _(const Tuple& t, const Separator& separator, Context& context)
{
_impl(t, separator, context, type<0>());
};
if (index)
context << separator;
if (requires_braces_t<Element>::value)
context << "(";
serialize(element, context);
if (requires_braces_t<Element>::value)
context << ")";
}
private:
template<size_t> struct type {};
template<typename Separator, size_t index>
static void _impl(const Tuple& t, const Separator& separator, Context& context, const type<index>&)
{
if (index)
context << separator;
const auto& entry = std::get<index>(t);
using entry_type = typename std::tuple_element<index, Tuple>::type;
if (requires_braces_t<entry_type>::value)
context << "(";
serialize(entry, context);
if (requires_braces_t<entry_type>::value)
context << ")";
_impl(t, separator, context, type<index + 1>());
}
template<typename Separator>
static void _impl(const Tuple& t, const Separator& separator, Context& context, const type<std::tuple_size<Tuple>::value>&)
{
}
};
template<typename Tuple, typename Separator, typename Context, size_t... Is>
auto interpret_tuple_impl(const Tuple& t, const Separator& separator, Context& context, const ::sqlpp::detail::index_sequence<Is...>&)
-> Context&
{
// Note: A braced-init-list does guarantee the order of evaluation according to 12.6.1 [class.explicit.init] paragraph 2 and 8.5.4 [dcl.init.list] paragraph 4.
// See for example: "http://en.cppreference.com/w/cpp/utility/integer_sequence"
// See also: "http://stackoverflow.com/questions/6245735/pretty-print-stdtuple/6245777#6245777"
// Beware of gcc-bug: "http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253", otherwise an empty swallow struct could be used
using swallow = int[];
(void) swallow{(interpret_tuple_element(std::get<Is>(t), separator, context, Is) ,0)...};
return context;
}
template<typename Tuple, typename Separator, typename Context>
auto interpret_tuple(const Tuple& t, const Separator& separator, Context& context)
-> decltype(tuple_interpreter_t<Context, Tuple>::_(t, separator, context))
-> Context&
{
return tuple_interpreter_t<Context, Tuple>::_(t, separator, context);
return interpret_tuple_impl(t, separator, context, ::sqlpp::detail::make_index_sequence<std::tuple_size<Tuple>::value>{});
}
}