single_use_lifetimes.rs

#![warn(single_use_lifetime)]
#![allow(dead_code)]
#![allow(unused_variables)]
 
fn a<'a>(x: &'a u32) { // Warning: used only once
}
 
fn b<'a>() -> &'a u32 { // OK: used only in return type
    &22
}
 
fn c<'a>(x: &'a u32) -> &'a u32 { // OK: used twice
    &22
}

fn d<'a>() { } // Warning: never used at all
 
struct Foo<'f> {
    data: &'f u32
}
 
impl<'f> Foo<'f> { // OK for *now* FIXME(#15872)
    fn inherent_a(&self) {
    }

    fn inherent_b<'a>(x: &'a u32) { // Warning for `'a` expected
    }
 
    fn inherent_c<'a>() -> &'a u32 { // OK: used only in return type
        &22
    }
 
    fn inherent_d<'a>(x: &'a u32) -> &'a u32 { // OK: used twice
        &22
    }
}

impl<'f> Foo<'f> { // OK
    fn new(data: &'f u32) -> Self {
        Foo { data }
    }
}

impl<'f> Iterator for Foo<'f> { // OK: used twice
    type Item = &'f u32;

    fn next<'g>(&'g mut self) -> Option<Self::Item> { // Warning for `'g`
        None
    }
} 

impl<'f> Foo<'f> { // OK: used twice
    fn get(&self) -> &'f u32 {
        self.data
    }
}

fn main() { }