Explain what variadic functions are and how they are supported in two languages of your choice (e.g., C/C++, Go, Java, Python). Cover calling conventions and how arguments are accessed by the callee, type-safety mechanisms (e.g., templates/generics vs. raw varargs), performance and stack/heap implications, and how to forward variadic arguments to another function. Implement a typesafe variadic logger that accepts key–value pairs and formats them efficiently; discuss pitfalls such as format-string vulnerabilities, boxing/reflection overhead, and ambiguity resolution. Provide tests and analyze complexity.