nlohmann::basic_json::merge_patch

void merge_patch(const basic_json& apply_patch);

The merge patch format is primarily intended for use with the HTTP PATCH method as a means of describing a set of modifications to a target resource's content. This function applies a merge patch to the current JSON value.

The function implements the following algorithm from Section 2 of RFC 7396 (JSON Merge Patch):

define MergePatch(Target, Patch):
  if Patch is an Object:
    if Target is not an Object:
      Target = {} // Ignore the contents and set it to an empty Object
    for each Name/Value pair in Patch:
      if Value is null:
        if Name exists in Target:
          remove the Name/Value pair from Target
      else:
        Target[Name] = MergePatch(Target[Name], Value)
    return Target
  else:
    return Patch

Thereby, Target is the current object; that is, the patch is applied to the current value.

Parameters

apply_patch (in): the patch to apply

Exception safety

Basic guarantee: if an exception is thrown during the operation, the JSON value may be partially modified.

Complexity

Linear in the lengths of apply_patch.

Notes

apply_patch may be #!cpp *this itself or refer to a value contained in #!cpp *this (for example, a subobject returned by #!cpp (*this)[key]); it is read as it was when merge_patch() was called, before any modification of #!cpp *this.

Examples

??? example

The following code shows how a JSON Merge Patch is applied to a JSON document.
 
```cpp
--8<-- "examples/merge_patch.cpp"
```

Output:

```json
--8<-- "examples/merge_patch.output"
```

Version history

Added in version 3.0.0.
Fixed use of freed or relocated memory when apply_patch is #!cpp *this or refers to a value contained in #!cpp *this, in version 3.13.0.

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