Implications of call as_str() to create new String

help
1

Hi folks,

I am trying to figure out the best way to replicate a string.

I have two methods, listed below.

Method 1 creates a new String by calling the as_str() function. Using method 1, am I correct in thinking that a string slice with a static lifetime will be created? If so, is s2 now dependant on s1 which lives on the heap?

Method 2 creates a new String by calling the clone() function. Using method 2, am I correct in thinking that s1 can go out of scope and it will have no effect on s2?

// Method 1
let s1 = String::from("hello, world");
let s2 = String::from(s1.as_str());

// Method 2
let s1 = String::from("hello, world");
let s2 = s1.clone();

Any guidance would be greatly appreciated.

1 Like
2

No. calling .as_str() produces a &str that is valid for as long as s1 is usable. Then, calling String::from() on that will copy the text data to a new heap allocation, so the resulting String in s2 can be used independently from s1

1 Like
3

Yes, that's correct for method 2. Cloning s1 is actually what the compiler will advise you to do if you've moved its value before trying to use it again.

4

Thanks for the quick reply.

So the &str value is copied to a new String and allocated space on the heap, that makes sense.

From a resource point of view is method 1 is slightly better?

5

Thanks for getting back to me, that makes sense.

6

They are exactly the same.