What is the primary function of @HttpPut in Salesforce?

The primary function of @HttpPut in Salesforce is to update existing records or create new records if they do not already exist. This HTTP method is part of the RESTful web services in Salesforce, conforming to the principles of REST architecture.

When a request is made using @HttpPut, it is designed to send a complete representation of a resource to be modified. If the resource (or record) specified in the request already exists in the system, the @HttpPut method updates it. Conversely, if the specified resource does not exist, the @HttpPut method can create a new instance of that resource. This dual capability is crucial for applications that need to efficiently manage resources via a consistent interface, allowing for both updates and resource creation in one action.

In contrast, other options present actions that do not align with the functionality of @HttpPut. Deleting records is associated with the HTTP DELETE method, while retrieving records corresponds to the HTTP GET method. The PATCH method, which is not the correct answer here, is focused on making partial updates to an existing resource rather than replacing it completely.