3.0.0

Breaking changes

• The default behavior for scanning integers is now d (decimal) instead of i (detect base from prefix).

// v3
auto result = scn::scan<int>("077", "{}");
// result->value() == 77
result = scn::scan<int>("078", "{}");
// result->value() == 78

// v2
auto result = scn::scan<int>("077", "{}");
// result->value() == 63
result = scn::scan<int>("078", "{}");
// result->value() == 7
// result->range() == "8"
// (Because of the '0' prefix, an octal number is expected,
//  and '8' is not a valid octal digit, so reading is stopped)

• A large part of the bundled <ranges>-implementation is removed.
  Only the parts strictly needed for the library are included.
  • The library no longer uses a stdlib provided <ranges>, even if available.
  • This cut down compile times massively for library consumers
  • You now may need to specialize scn::ranges::enable_borrowed_range for your own range types,
    even if you've already specialized std::ranges::enable_borrowed_range.
    Specializations of std::basic_string_view are already borrowed out of the box.

// std::span is a borrowed_range,
// but scnlib doesn't know about it
auto result = scn::scan<...>(std::span{...}, ...);
// decltype(result->range()) is scn::ranges::dangling

namespace scn::ranges {
template <typename T, size_t E>
inline constexpr bool enable_borrowed_range<std::span<T, E>> = true;
}

auto result = scn::scan<...>(std::span{...}, ...);
// decltype(result->range()) is a scn::ranges::subrange<const T*>

• scn::span is removed
• scan_arg_store and borrowed_subrange_with_sentinel are removed from the public interface
• scan_arg_store is changed to be non-copyable and non-movable, for correctness reasons
  (it holds references to itself, copying and moving would be needlessly expensive)
• The interface of make_scan_result is changed to take a tuple instead of the now unmovable scan_arg_store.

// v3
auto args = make_scan_args<scan_context, Args...>();
auto result = vscan(source, format, args);
return make_scan_result(std::move(result), std::move(args.args()));

// v2
auto args = make_scan_args<scan_context, Args...>();
auto result = vscan(source, format, args);
return make_scan_result(std::move(result), std::move(args));

• The meaning of the "width" field in format specifiers is changed to mean the minimum field width
  (like in std::format), instead of the maximum (sort of like in scanf)

// v3
auto result = std::scan<int>("123", "{:2}");
// result->value() == 123
// result->range() == ""

// v2
auto result = std::scan<int>("123", "{:2}");
// result->value() == 12
// result->range() == "3"

Features

• The "precision" field is added as a format specifier,
  which specifies the maximum fields width to scan (like in std::format)

// Scan up to 2 width units
auto result = scn::scan<int>("123", "{:.2}");
// result->value() == 12
// result->range() == "3"

• Support for field fill and alignment is added.
  This interacts well with the new width and precision fields

// Read an integer, aligned to the right ('>'), with asterisks ('*')
auto result = std::scan<int>("***42", "{:*>}");
// result->value() == 42
// result->range() == ""

// Read an integer, aligned to the left ('<'), with whitespace (default),
// with a maximum total width of 3
auto result = std::scan<int>("42  ", "{:<.3}");
// result->value() == 42
// result->range() == " "

• In general, there seems to be a ~10% to 20% improvement in run-time performance.

Changes

• The dependency on simdutf is removed. The library now has no external dependencies to compiled libraries
  (FastFloat, an internal dependency, is a header-only library)
• The number of source files is dramatically decreased: there are now just the public headers,
  a private implementation header, and a private implementation source file. This cuts down the time needed to
  compile the library, and any user code including it to a half (yes, really!)

Fixes

• Fix skipping of multiple characters of whitespace in the format string (reported in #116, thanks @Jonathan-Greve (Jonathan Bjørn Greve))

Full Changelog: v2.0.3...v3.0.0