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Docs: Fix wrong code usage in the Value access section of json_pointer.md #4255

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merged 1 commit into from
Apr 13, 2024

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The code usage demo in the Value access section of the JSON Pointer document does not work correctly

https://json.nlohmann.me/features/json_pointer/#value-access

```cpp
// the JSON value from above
auto j = json::parse(R"({
"array": ["A", "B", "C"],
"nested": {
"one": 1,
"two": 2,
"three": [true, false]
}
})");
// access values
auto val = j["/"_json_pointer]; // {"array":["A","B","C"],...}
auto val1 = j["/nested/one"_json_pointer]; // 1
auto val2 = j.at[json::json_pointer("/nested/three/1")]; // false
auto val3 = j.value[json::json_pointer("/nested/four", 0)]; // 0
```

There are 3 mistakes in the code above:

  1. (line 74) The json pointer "/" does not point to the root object. Instead, it points to the value with an empty string as the key at the root object. It should be replaced with json pointer ""

    // empty string access
    CHECK(j[json::json_pointer("/")] == j[""]);

    // the whole document
    CHECK(j[json::json_pointer()] == j);
    CHECK(j[json::json_pointer("")] == j);

  2. (line 76) Incorrect usage of nlohmann::basic_json::at. It's a function and does not support the [] operator

  3. (line 77) Incorrect usage of nlohmann::basic_json::value. It's a function and does not support the [] operator. Additionally, the argument 0 as the default value for the value function is incorrectly placed

This PR resolves these 3 mistakes and makes the demo code work correctly


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  • Changes are described in the pull request, or an existing issue is referenced.
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Coverage Status

coverage: 100.0%. remained the same
when pulling 4d6cae7 on Fallen-Breath:patch-1
into a259ecc on nlohmann:develop.

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Looks good to me.

@nlohmann nlohmann added this to the Release 3.11.4 milestone Apr 13, 2024
@nlohmann nlohmann merged commit 8c391e0 into nlohmann:develop Apr 13, 2024
107 of 110 checks passed
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3 participants