How to swap two strings

help
1

I've just finished reading " What Is Ownership?" section of the book.
I remember writing a C swap function to swap two integers that involves using a temp variable and parameters having to be pointers.
Now I want to use Rust to swap two different strings. (That seems impossible in C)
Here is the code.

fn main() {
    let s1 = String::from("Hello");
    let s2 = String::from("World");
    println!("{} {}", s1, s2);
    let (s1, s2) = swap(s1, s2);
    println!("{} {}", s1, s2);
}
fn swap(s1: String, s2: String) -> (String, String) {
    (s2, s1) 
}

After compiling and running, I get what I want to see happen.
But the code I write makes me feel weird as no temp variable is used and the s1 s2 which are assigned the second time are different from the previous s1 and s2 .
I think that's not actually swapped.
Any better ideas to write swap strings?

2

The standard library has a general-purpose swap function you can use:

std::mem::swap(&mut s1, &mut s2);

If you use this function and compile your code in release mode, you can see that it does indeed allocate and use a temporary variable that is 24 bytes large, just as big as a String. Check it out here.

1 Like
3

How would this differ in C from the case of swapping integers? Strings are just pointers, and can be assigned just as integers are.

4

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