Say I have the following struct:
struct MyStruct
{
int field1;
float field2;
};
I would like to obtain the number of fields in the struct using boost-hana.
#include <boost/hana/adapt_struct.hpp>
BOOST_HANA_ADAPT_STRUCT(MyStruct, position, field1, field2);
// this code does not work:
constexpr std::size_t NUMBER_OF_FIELDS = boost::hana::length<MyStruct>();
static_assert(NUMBER_OF_FIELDS == 2);
How to get the number of fields in a boost-hana adapted struct?
Hana specifically aims to simplify meta-programming by lifting type functions to the constexpr domain. In plain English: you shouldn't be using length<>
as a "type function template" but as a normal function:
struct MyStruct
{
int position;
int field1;
float field2;
};
#include <boost/hana.hpp>
BOOST_HANA_ADAPT_STRUCT(MyStruct, position, field1, field2);
constexpr std::size_t NUMBER_OF_FIELDS = boost::hana::size(MyStruct{});
static_assert(NUMBER_OF_FIELDS == 3);
int main(){}