Lifetime confusion about "&c.tostring()"

I'm reading "rust for rustaceans",below is an example in the book:

struct StrSplit<'s, 'p> {
    delimiter: &'p str,
    document: &'s str,
impl<'s, 'p> Iterator for StrSplit<'s, 'p> {
    type Item = &'s str;
    fn next(&mut self) -> Option<Self::Item> {
fn str_before(s: &str, c: char) -> Option<&str> {
    StrSplit {
        document: s,
        delimiter: &c.to_string(),

I'm wondering why the &c.to_string() won't throw "temporary value dropped while borrowed" error?I assume that c.to_string() will return a String value and will be dropped immediately.
Appreciate anyone who reply.

1 Like

Temporary lifetime extension. The String drops after next() is executed but before the result at the call site instantiates. Edit: see next post.

I'll clarify: this is not temporary lifetime extension. This is regular temporary lifetime.

A temporary lives until the end of a statement or, if it's in the last expression of a function (as it is in this case) then it lives until the end of the function.


Yep, my bad.

It makes sense! Thanks for your reply

Thanks for your reply, which helps extend my understanding of lifetime.