again - borrowed value does not live long enough

Question

I can't understand what's going on here:

struct MyStruct<'a> {
  field1: i32,
  field2: &'a str,
}

impl<'a> MyStruct<'a> {
    fn foo(var1: i32, var2: i32, var3: &str) -> &'a str {
      &format!("{} {} {} fdsfdsfd", var1, var2, var3)
    }
}

fn main() {
}

Should I somehow return str with lifetime 'a from foo? If not, how to fix it?

score 3 · Answer 1 · answered Aug 14 '15 at 07:55

3

You’re creating a string and then trying to return a reference to it, but the string that you’re returning a reference to is not stored anywhere. You should return the String itself.

answered Aug 14 '15 at 07:55

Chris Morgan

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only String? no another way? – imatahi Aug 14 '15 at 09:34
meaning, no way to return `&str`? – imatahi Aug 14 '15 at 10:22
@imatahi: you can’t have a reference to something that doesn’t exist. – Chris Morgan Aug 14 '15 at 13:00
Ok. What do you mean by "You’re creating a string" - where exactly is it created? – imatahi Aug 14 '15 at 15:38
and how come then this is working `fn abc() -> &'static str { "fdsfds343432fdsfd" }`? – imatahi Aug 14 '15 at 18:45
@imatahi `format!` allocates a brand new `String`. Your `&'static str ` lives for the entire life of the program (it's "owned" by the compiled code). After the function returns, nothing owns your created string, so it is dropped and any references to it become invalid. – Shepmaster Aug 15 '15 at 12:57
so how about "you can’t have a reference to something that doesn’t exist." in case of `&'static str`? – imatahi Aug 15 '15 at 14:32
@imatahi: the underlying string is stored in the compiled program. – Chris Morgan Aug 20 '15 at 20:06

again - borrowed value does not live long enough

1 Answers1