Q: What is the difference between String and &str in Rust?

Answer:

In Rust, String and &str are both used to handle string data, but they have distinct differences in how they manage memory and handle ownership:

1. String:

   • It is an owned type.
   • It is stored on the heap, meaning its size can grow or shrink at runtime.
   • When a String goes out of scope, its memory is automatically freed (dropped).
   • You can mutate it (if it's declared mut), e.g., by pushing new characters or strings to it.

2. &str (String Slice):

   • It is a borrowed type (a reference).
   • It represents a view into a block of memory that contains a string (which could be on the heap, stack, or hardcoded in the binary as a static string).
   • It does not have ownership of the data it points to; it merely looks at it temporarily.
   • It is immutable by default and its size is fixed.

Example:

fn main() {
    // A String (heap-allocated, owned, growable)
    let mut my_string = String::from("Hello");
    my_string.push_str(", world!");

    // A &str (string slice, borrowed, fixed-size view)
    let my_slice: &str = &my_string[0..5]; // Borrows "Hello"
    
    // Hardcoded string literals are also of type &str (specifically &'static str)
    let static_str: &str = "I am stored in the binary";
}