amorfo77/json
1
0
Fork 0
mirror of https://github.com/nlohmann/json.git synced 2026-07-09 12:05:10 +00:00
Code Issues Packages Projects Releases Wiki Activity

📡 Document cross-basic_json conversion limitation (#3425)

Browse Source 
When converting objects or strings between different basic_json specializations,
the target's object_t::key_type or string_t must be directly constructible from
the source's corresponding type. If this requirement is not met, the conversion
silently falls back to the array-conversion path, producing incorrect results.

This documents the limitation and provides references to issue #3425, which tracks
this behavior. The comment in unit-alt-string.cpp is clarified to reference the
known limitation with a link to the issue, and suggests the parse() workaround.

Fixes #3425 (documentation; full fix deferred pending type-trait redesign)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-07-08 21:10:01 +02:00
parent 366f3d26e5
commit 58a637d79c
4 changed files with 36 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/src/unit-alt-string.cpp
+6 -8
View File
@@ -322,14 +322,12 @@ TEST_CASE("alternative string type")
SECTION("JSON pointer")
{
// conversion from json to alt_json fails to compile (see #3425);
// attempted fix(*) produces: [[['b','a','r'],['b','a','z']]] (with each char being an integer)
// (*) disable implicit conversion for json_refs of any basic_json type
// alt_json j = R"(
// {
// "foo": ["bar", "baz"]
// }
// )"_json;
// Direct conversion from a json literal to alt_json is not supported due to issue #3425:
// alt_json's string_t (alt_string) is not directly constructible from std::string, so the
// cross-basic_json conversion falls back to the array-conversion path, incorrectly representing
// objects as arrays of [key, value] pairs and strings as arrays of character codes.
// See https://github.com/nlohmann/json/issues/3425 for details.
// Workaround: use alt_json::parse() instead of implicit conversion.
auto j = alt_json::parse(R"({"foo": ["bar", "baz"]})");
CHECK(j.at(alt_json::json_pointer("/foo/0")) == j["foo"][0]);