Can't access context args() directly in 11.1.0 #4307
Description
I have a use case where my custom formatter needs to format to a buffer and then remove either the front or the back of the buffer.
Example on 11.0.0 where this works: https://godbolt.org/z/96KeTG9bG
In order to do this, I create a new format_context using the original context's args() and locale() in the format function, but with a temporary append buffer. I then can output just a chunk of the buffer.
With 11.1.0 there was some code cleanup in 1416eda that removed the accessor for args_ which breaks my use case. In order for my code to work I either need:
- An accessor to
args_andlocale_(locale()is still available) - A method to replace
out_ - A constructor to make a new context from a
const context&and a newappender
Sample found on godbolt:
#include <fmt/core.h>
#include <string_view>
template<class T>
class truncator
{
const T& t;
int c;
public:
constexpr truncator(const T& data_, const int count_) noexcept
: t{data_}, c{count_}
{}
constexpr const T& data() const noexcept { return t; }
constexpr int count() const noexcept { return c; }
};
template<class T>
constexpr truncator<T> trunc(const T& data, int count) noexcept
{
return {data, count};
}
namespace fmt
{
template<typename T, typename Char>
struct formatter<truncator<T>, Char> : public formatter<T, Char>
{
public:
template<typename FormatContext>
auto format(const truncator<T>& v, FormatContext& ctx) const
{
basic_memory_buffer<Char> buffer;
format_context ctx2(appender{buffer}, ctx.args(), ctx.locale());
formatter<T, Char>::format(v.data(), ctx2);
auto beg = buffer.begin();
auto end = buffer.end();
const auto size = std::distance(beg, end);
const auto abs_count = v.count() < 0 ? -v.count() : v.count();
if(v.count() != 0 && size > abs_count) {
const auto size_remove = size - abs_count;
if(v.count() > 0) {
beg = std::next(beg, size_remove);
} else {
end = std::prev(end, size_remove);
}
}
ctx.advance_to(std::copy(beg, end, ctx.out()));
return ctx.out();
}
};
}
int main() {
fmt::print(">{0}<\n", trunc(1234, -2));
fmt::print(">{0}<\n", trunc(1234, 2));
}