rust - trait with functions that return an iterator -

i'm trying build trait functions return iterator.

my simple example looks this:

pub trait traita {     fn things(&self) -> iterator<item=&u8>; }  fn foo<a: traita>(a: &a) {     x in a.things() { } } 

which not work because iterator size type not known @ compile time.

rust's libstd has 1 implementation of this, trait intoiterator.

/// conversion `iterator` pub trait intoiterator {     /// type of elements being iterated     type item;      /// container iterating on elements of type `item`     type intoiter: iterator<item=self::item>;      /// consumes `self` , returns iterator on     fn into_iter(self) -> self::intoiter; } 

the trait has peculiar by-value (self) formulation able express both “into iterator” , “borrow iterator” semantics.

demonstrated hashmap's intoiterator implementations. (they use hashmap's iterator structs iter , intoiter.) what's interesting here trait implemented type &hashmap<k, v, s> express “borrow iterator”.

impl<'a, k, v, s> intoiterator &'a hashmap<k, v, s>     k: eq + hash, s: hashstate {     type item = (&'a k, &'a v);     type intoiter = iter<'a, k, v>;      fn into_iter(self) -> iter<'a, k, v> {         self.iter()     } }  impl<k, v, s> intoiterator hashmap<k, v, s>     k: eq + hash, s: hashstate {     type item = (k, v);     type intoiter = intoiter<k, v>;      /// creates consuming iterator, is, 1 moves each key-value     /// pair out of map in arbitrary order. map cannot used after     /// calling this.     fn into_iter(self) -> intoiter<k, v> {         /* ... */     } }