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+# 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)](https://tools.ietf.org/html/rfc7396):
+
+```
+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
+
+## Complexity
+
+Linear in the lengths of `apply_patch`.
+
+## Examples
+
+Example
+
+The following code shows how a JSON Merge Patch is applied to a JSON document.
+
+```
+#include <iostream>
+#include <nlohmann/json.hpp>
+#include <iomanip> // for std::setw
+
+using json = nlohmann::json;
+using namespace nlohmann::literals;
+
+int main()
+{
+    // the original document
+    json document = R"({
+                "title": "Goodbye!",
+                "author": {
+                    "givenName": "John",
+                    "familyName": "Doe"
+                },
+                "tags": [
+                    "example",
+                    "sample"
+                ],
+                "content": "This will be unchanged"
+            })"_json;
+
+    // the patch
+    json patch = R"({
+                "title": "Hello!",
+                "phoneNumber": "+01-123-456-7890",
+                "author": {
+                    "familyName": null
+                },
+                "tags": [
+                    "example"
+                ]
+            })"_json;
+
+    // apply the patch
+    document.merge_patch(patch);
+
+    // output original and patched document
+    std::cout << std::setw(4) << document << std::endl;
+}
+```
+
+Output:
+
+```
+{
+    "author": {
+        "givenName": "John"
+    },
+    "content": "This will be unchanged",
+    "phoneNumber": "+01-123-456-7890",
+    "tags": [
+        "example"
+    ],
+    "title": "Hello!"
+}
+```
+
+## See also
+
+- [RFC 7396 (JSON Merge Patch)](https://tools.ietf.org/html/rfc7396)
+- [patch](https://json.nlohmann.me/api/basic_json/patch/index.md) apply a JSON patch
+
+## Version history
+
+- Added in version 3.0.0.