deploy: fe0299545a

api/basic_json/basic_json.md

@@ -82,7 +82,13 @@ basic_json(basic_json&& other) noexcept;
 4. This is a constructor for existing `basic_json` types. It does not hijack copy/move constructors, since the parameter
    has different template arguments than the current ones.
 
-    The constructor tries to convert the internal `m_value` of the parameter.
+    The constructor tries to convert the internal `m_value` of the parameter. Each member value (object, array, string,
+    etc.) is serialized via the corresponding `to_json()` overload. For objects and strings, the conversion requires
+    that the *target* `basic_json` type's `object_t::key_type` (or `string_t`) be directly constructible from the
+    *source* type's corresponding member type via `is_constructible`. If this requirement is not met, the conversion
+    does not fail to compile; instead, it silently falls back to the array-conversion path, which represents objects
+    as arrays of `[key, value]` pairs and strings as arrays of character codes. This is a known limitation tracked in
+    [issue #3425](https://github.com/nlohmann/json/issues/3425).
 
 5. Creates a JSON value of type array or object from the passed initializer list `init`. In case `type_deduction` is
    `#!cpp true` (default), the type of the JSON value to be created is deducted from the initializer list `init`
@@ -146,6 +152,11 @@ basic_json(basic_json&& other) noexcept;
 
     - `BasicJsonType` is a `basic_json` type.
     - `BasicJsonType` has different template arguments than `basic_json_t`.
+    
+    **Note:** For cross-`basic_json` conversions to produce correct results, the target `basic_json`'s
+    `object_t::key_type` and `string_t` must be directly constructible from the source `basic_json`'s
+    corresponding types. See the description of overload (4) above for details on what happens when
+    this requirement is not met.
 
 `U`:
 :   `uncvref_t<CompatibleType>`

api/basic_json/basic_json/index.md

@@ -67,7 +67,7 @@ basic_json(basic_json&& other) noexcept;
 
 1. This is a constructor for existing `basic_json` types. It does not hijack copy/move constructors, since the parameter has different template arguments than the current ones.
 
-   The constructor tries to convert the internal `m_value` of the parameter.
+   The constructor tries to convert the internal `m_value` of the parameter. Each member value (object, array, string, etc.) is serialized via the corresponding `to_json()` overload. For objects and strings, the conversion requires that the *target* `basic_json` type's `object_t::key_type` (or `string_t`) be directly constructible from the *source* type's corresponding member type via `is_constructible`. If this requirement is not met, the conversion does not fail to compile; instead, it silently falls back to the array-conversion path, which represents objects as arrays of `[key, value]` pairs and strings as arrays of character codes. This is a known limitation tracked in [issue #3425](https://github.com/nlohmann/json/issues/3425).
 
 1. Creates a JSON value of type array or object from the passed initializer list `init`. In case `type_deduction` is `true` (default), the type of the JSON value to be created is deducted from the initializer list `init` according to the following rules:
 
@@ -118,6 +118,11 @@ basic_json(basic_json&& other) noexcept;
 ```
 - `BasicJsonType` is a `basic_json` type.
 - `BasicJsonType` has different template arguments than `basic_json_t`.
+
+**Note:** For cross-`basic_json` conversions to produce correct results, the target `basic_json`'s
+`object_t::key_type` and `string_t` must be directly constructible from the source `basic_json`'s
+corresponding types. See the description of overload (4) above for details on what happens when
+this requirement is not met.
 ```
 
 `U`: : `uncvref_t<CompatibleType>`

api/basic_json/object_t.md

@@ -93,6 +93,15 @@ alphabetical order as `std::map` with `std::less` is used by default. Please not
 [RFC 8259](https://tools.ietf.org/html/rfc8259), because any order implements the specified "unordered" nature of JSON
 objects.
 
+#### Cross-`basic_json` conversion requirements
+
+When converting an object from one `basic_json` specialization to another via the
+[converting constructor](basic_json.md#overload-4), the target `object_t`'s `key_type` must be
+directly constructible from the source `basic_json`'s `string_t` type (or more generally, from the
+source object's key type). If this requirement is not met, the conversion does not fail; instead,
+the object is silently converted as an array of key-value pairs, which is incorrect. See
+[issue #3425](https://github.com/nlohmann/json/issues/3425) for details and an example.
+
 ## Examples
 
 ??? example

api/basic_json/object_t/index.md

@@ -74,6 +74,10 @@ Objects are stored as pointers in a `basic_json` type. That is, for any access t
 
 The order name/value pairs are added to the object are *not* preserved by the library. Therefore, iterating an object may return name/value pairs in a different order than they were originally stored. In fact, keys will be traversed in alphabetical order as `std::map` with `std::less` is used by default. Please note this behavior conforms to [RFC 8259](https://tools.ietf.org/html/rfc8259), because any order implements the specified "unordered" nature of JSON objects.
 
+#### Cross-`basic_json` conversion requirements
+
+When converting an object from one `basic_json` specialization to another via the [converting constructor](https://json.nlohmann.me/api/basic_json/basic_json/#overload-4), the target `object_t`'s `key_type` must be directly constructible from the source `basic_json`'s `string_t` type (or more generally, from the source object's key type). If this requirement is not met, the conversion does not fail; instead, the object is silently converted as an array of key-value pairs, which is incorrect. See [issue #3425](https://github.com/nlohmann/json/issues/3425) for details and an example.
+
 ## Examples
 
 Example