error[E0277]: the size for values of type `str` cannot be known at compilation time

Workarounds

1. 95% success Use &str for borrowed string references (most common fix)

   // Before (error):
   fn greet(name: str) { // E0277: str is not Sized
       println!("Hello, {name}");
   }
   
   // After: use a reference
   fn greet(name: &str) {
       println!("Hello, {name}");
   }
   
   // For struct fields:
   struct Config<'a> {
       name: &'a str,  // Borrowed string slice with lifetime
   }
   
   let cfg = Config { name: "production" };

   Sources: https://doc.rust-lang.org/book/ch04-03-slices.html#string-slices

2. 93% success Use String for owned string data

   // When you need ownership (e.g., storing in a struct without lifetimes):
   struct User {
       name: String,  // Owned, heap-allocated, Sized
   }
   
   impl User {
       fn new(name: &str) -> Self {
           User { name: name.to_string() }
       }
   }
   
   // For function parameters that need ownership:
   fn store_name(name: String) {
       // name is owned and can be stored
   }

   Sources: https://doc.rust-lang.org/book/ch08-02-strings.html

3. 80% success Use Box<str> for owned string data with minimal overhead

   // Box<str> is a thin pointer + length, slightly smaller than String
   // (no capacity field). Useful for immutable owned strings:
   let boxed: Box<str> = "hello".into();
   let boxed: Box<str> = String::from("hello").into_boxed_str();
   
   // In generic contexts with ?Sized bound:
   fn print_it<T: AsRef<str> + ?Sized>(val: &T) {
       println!("{}", val.as_ref());
   }
   print_it("literal");        // &str
   print_it(&String::from("owned")); // &String

   Sources: https://doc.rust-lang.org/std/boxed/struct.Box.html