Why is mut required for fn param when variable defined with mut

The following code works the way expected, however I'm hoping to find a good reason why the "mut" qualifier is required on the first parameter when calling the add_employee fn.

Since the variable emps is defined with mut, and the signature expects it, why is that not sufficient?

struct Employee {          name: String,          age: u16,  }  impl Employee {      fn new() -> Employee {          Employee {              name: "Julia".to_string(),              age: 15          }      }  }    fn add_employee(emps: &mut Vec<Employee>, emp: Employee) {      emps.push(emp);  }    fn main() {      let mut emps: Vec<Employee> = Vec::new();      add_employee(&mut emps, Employee::new());   // why is mut required here?            println!("name = {}, age = {}", emps[0].name, emps[0].age);  }  

https://stackoverflow.com/questions/67248907/why-is-mut-required-for-fn-param-when-variable-defined-with-mut April 25, 2021 at 09:18AM