Failing to implement IntoIterator because if lifetime issues

Failure to set type lifetime

vec3.rs:46:6: 46:8 error: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates [E0207]
vec3.rs:46 impl<'a> IntoIterator for V3 {
                ^~
vec3.rs:46:6: 46:8 help: run `rustc --explain E0207` to see a detailed explanation
error: aborting due to previous error

test.rs

use std::ops::Index;
use std::iter::IntoIterator;

#[derive(Copy, Clone, Default)]
pub struct V3 {
    pub x: f32,
    pub y: f32,
    pub z: f32,
}

impl Index<i32> for V3
{
    type Output = f32;
    fn index(&self, index: i32) -> &f32 {
        match index {
            0 => &self.x,
            1 => &self.y,
            2 => &self.z,
            _ => panic!(),
        }
    }
}

struct V3Iter<'a> {
    v: &'a V3,
    i: i32,
}

impl<'a> Iterator for V3Iter<'a> {
    type Item = f32;
    fn next(&mut self) -> Option<f32> {
        let result = if self.i < 3 {
            Some(self.v[self.i])
        } else {
            None
        };

        self.i += 1;

        result
    }
}

impl <'a> IntoIterator for V3 {
    type Item = f32;
    type IntoIter = V3Iter<'a>;
    fn into_iter(&'a self) -> Self::IntoIter {
        V3Iter { v: &self, i: 0 }
    }
}

fn main(){
    let vec = V3{x:212.0, y: 3121.0, z:32432.0};
    let iter = V3Iter{v:&vec, i:0};
    for x in iter{
        println!("- {}", x);
    }

}