In Rust, the `ref` keyword is used in pattern matching and function parameters to create a reference to a value rather than taking ownership or borrowing it directly. It is primarily used to work with references in specific contexts. Here are two common use cases for the `ref` keyword:

1. Pattern Matching :
   * When pattern matching on a value, the `ref` keyword allows you to bind a reference to the matched value instead of taking ownership or borrowing it.
   * It is particularly useful when you want to modify or access the value through a reference without taking ownership.
   * Here's an example that demonstrates the use of `ref` in a pattern:

     fn main() {
         let value = 42;
         
         match value {
             ref r => println!("Reference to value: {}", r),
         }
     }​

     In this example, the `ref` keyword is used to bind a reference to the value `42` during pattern matching. The reference `r` is then printed, demonstrating that we can access the value through a reference without taking ownership. 2. Function Parameters :
   * In function parameters, the `ref` keyword allows you to accept a reference to a value rather than taking ownership or borrowing it directly.
   * It is useful when you want to work with a reference within the function without taking ownership of the value.
   * Here's an example that shows the use of `ref` in function parameters:

     fn process_reference(ref r: &i32) {
         // Use the reference without taking ownership
         println!("Value: {}", r);
     }
     
     fn main() {
         let value = 42;
         process_reference(&value);
     }​

     In this example, the `process_reference` function accepts a reference `ref r` to an `i32` value. The function can then work with the reference without taking ownership of the value, allowing the caller to retain ownership.

The `ref` keyword is not commonly used in everyday Rust code, but it can be handy in certain situations where you specifically need to work with references in pattern matching or function parameters. It allows you to manipulate and access values through references without transferring ownership or borrowing the value directly.