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Documentation review: exceptions from binary-format hardening, and tuple reference types (#5359)

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* 📝 Document exceptions newly thrown by the binary-format hardening

A round of binary-format input validation (#5274, #5284, #5287, #5332)
added new failure modes without updating exceptions.md, and left two
descriptions factually narrower than the code:

- parse_error.110 said "CBOR or MessagePack"; BSON and UBJSON also
  throw it. Generalized, and added the BSON EOF example (#5332).
- parse_error.112: added the BSON document-size mismatch example
  (#5287).
- parse_error.113 said "while parsing a map key", but its own existing
  UBJSON char example already contradicted that. Broadened to cover
  invalid length specifications, and added the negative-string-length
  example (#5284).
- out_of_range.408 said "of an UBJSON array or object"; CBOR now throws
  it too (#5274). Generalized and added both CBOR examples.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* 📝 Correct which types may be referenced in a tuple extraction

The note added in #5271 said a referenced type must be one the library
stores "or an arithmetic type it can convert to/from". The parenthetical
is wrong: is_compatible_reference_type requires an exact match against
the stored types, so std::tuple<int&> is rejected by static_assert even
though int converts fine as a value. Only the value case is permissive.

Spell out the eight admissible types, give the int& counter-example, and
separate the reference restriction from by-value conversion.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-08-04 08:45:18 +02:00
committed by GitHub
parent 1c63a120b6
commit 173f2a7407
2 changed files with 32 additions and 7 deletions
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docs/mkdocs/docs/features/conversions.md
+8 -2
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@@ -66,8 +66,14 @@ auto t = j.get<std::tuple<double, std::string, int>>(); // {1.0, "hello", 42}
std::get<1>(refs) = "world"; // modifies j[1] in place
```
A referenced type must be one the library actually stores (or an arithmetic type it can convert to/from);
otherwise this is a compile error.
A referenced element must name the type the library actually *stores* — one of [`boolean_t`](../api/basic_json/boolean_t.md),
[`number_integer_t`](../api/basic_json/number_integer_t.md), [`number_unsigned_t`](../api/basic_json/number_unsigned_t.md),
[`number_float_t`](../api/basic_json/number_float_t.md), [`string_t`](../api/basic_json/string_t.md),
[`binary_t`](../api/basic_json/binary_t.md), [`array_t`](../api/basic_json/array_t.md), or
[`object_t`](../api/basic_json/object_t.md). There is nothing else to refer to, so a reference to any other type is a
compile error even when a conversion would exist: `#!cpp std::tuple<int&>` is rejected, because the library stores a
`#!cpp number_integer_t` (`#!cpp std::int64_t` by default) and not an `#!cpp int`. This restriction applies only to
reference elements — a plain `#!cpp std::tuple<int>` converts by value as usual.
## Implicit conversions