Error using boost::from_block_range on member dynamic_bitset, but not on local dynamic_bitset

Question

I am attempting to convert a std::vector<uint8_t> into a boost::dynamic_bitset. I can achieve the inverse of this using the following code, where values is a class member function defined as boost::dynamic_bitset<uint8_t> values.

std::vector<uint8_t> payload;
boost::to_block_range(values, std::back_inserter(payload));

However, I can't figure out how to do the inverse of it. The following compiles:

void MyClass::decode(std::vector<uint8_t> payload) const
{
    boost::dynamic_bitset<uint8_t> bits(payload.size() * 8);
    boost::from_block_range(payload.begin(), payload.end(), bits);
}

If I replace the bits local scoped-variable with the values class member variable (which from all indications are the same exact type, boost::dynamic_bitset<uint8_t>), I get the following compiler error:

error: no matching function for call to ‘from_block_range(std::vector<unsigned char>::iterator, std::vector<unsigned char>::iterator, const boost::dynamic_bitset<unsigned char>&)’ boost::from_block_range(payload.begin(), payload.end(), values);

Answer 1

Your decode method is marked const, but you are attempting to modify class member variable values.

Either remove the const or mark values mutable

For example:

#include <cstdint>
#include <vector>
#include "boost/dynamic_bitset.hpp"

struct foo
{
    void do_the_thing()
    {
        std::vector<uint8_t> payload{1, 2, 3, 4};
        bits = boost::dynamic_bitset<uint8_t>(payload.size() * 8);
        boost::from_block_range(payload.begin(), payload.end(), bits);
    }
    
    boost::dynamic_bitset<uint8_t> bits;
};

int main()
{
    foo f;
    f.do_the_thing();
}