From gregmarr's review of #5622:
- count() counts every member with the key, so count(key) > 1 detects
duplicate keys; it was contains() as 0/1 before.
- get_to() passes types that get<T>() does not convert directly to
from_json with the existing value, as basic_json::get_to() does, so that
a from_json which sets only the fields present keeps the others.
- array_index() checks the empty token and "-" first; the results are
unchanged.
- Docs: no "if an exception is thrown" where a view never changes
anything; the borrowed source must also stay unmodified; items() on a
temporary view is safe; back()/front() notes shortened; the basic_json
see-also entries say how the view's results can differ.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Give basic_json_view the read-only access functions of basic_json:
operator[] and at() with keys and indices, front()/back(), find(),
contains(), count(), begin()/end() and cbegin()/cend(), items()
with structured bindings from C++17 on, and type_name().
Exceptions have the ids and messages of the const functions of
basic_json. Where basic_json has undefined behavior the view
answers safely: operator[] with a missing key or an out-of-range
index returns a discarded view, and front()/back() of an empty
container throw invalid_iterator.214. Objects are iterated in
document order, and all members are visited; duplicate-key lookups
find the first member (as yyjson and simdjson do), while parse(),
materialize(), and the map conversions keep the last value, as
parse() does. Keys of up to 16 bytes are compared with two
overlapping loads.
Add value conversions: get<T>()/get_to() for arithmetic types,
bool, nullptr_t, strings (std::basic_string copied,
string_view_t without a copy), BasicJsonType, views, std::vector,
and maps with string keys; get_string() for the string without a
copy; number_token() for the number exactly as written in the
source; value() with keys and JSON pointers; and operator[]/at()/
contains() with JSON pointers. Everything else, including types
with from_json(), goes through materialize() of that subtree.
get<T>() of arithmetic types is inlined down to the conversion, so
reading an integer needs no call.
detail::json_pointer_access exposes a pointer's reference tokens
to code outside basic_json.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann