tweaks to core::iterator

src/libcore/iterator.rs

@@ -47,10 +47,10 @@ pub trait IteratorUtil<A> {
     fn advance(&mut self, f: &fn(A) -> bool);
     #[cfg(not(stage0))]
     fn advance(&mut self, f: &fn(A) -> bool) -> bool;
-    fn to_vec(self) -> ~[A];
-    fn nth(&mut self, n: uint) -> A;
-    fn first(&mut self) -> A;
-    fn last(&mut self) -> A;
+    #[cfg(not(stage0))]
+    fn to_vec(&mut self) -> ~[A];
+    fn nth(&mut self, n: uint) -> Option<A>;
+    fn last(&mut self) -> Option<A>;
     fn fold<B>(&mut self, start: B, f: &fn(B, A) -> B) -> B;
     fn count(&mut self) -> uint;
     fn all(&mut self, f: &fn(&A) -> bool) -> bool;
@@ -147,47 +147,30 @@ impl<A, T: Iterator<A>> IteratorUtil<A> for T {
         }
     }
 
+    #[cfg(not(stage0))]
     #[inline(always)]
-    fn to_vec(self) -> ~[A] {
-        let mut v = ~[];
-        let mut it = self;
-        for it.advance() |x| { v.push(x); }
-        return v;
+    fn to_vec(&mut self) -> ~[A] {
+        iter::to_vec::<A>(|f| self.advance(f))
     }
 
-    /// Get `n`th element of an iterator.
+    /// Return the `n`th item yielded by an iterator.
     #[inline(always)]
-    fn nth(&mut self, n: uint) -> A {
-        let mut i = n;
+    fn nth(&mut self, mut n: uint) -> Option<A> {
         loop {
             match self.next() {
-                Some(x) => { if i == 0 { return x; }}
-                None => { fail!("cannot get %uth element", n) }
+                Some(x) => if n == 0 { return Some(x) },
+                None => return None
             }
-            i -= 1;
+            n -= 1;
         }
     }
 
-    // Get first elemet of an iterator.
+    /// Return the last item yielded by an iterator.
     #[inline(always)]
-    fn first(&mut self) -> A {
-        match self.next() {
-            Some(x) => x ,
-            None => fail!("cannot get first element")
-        }
-    }
-
-    // Get last element of an iterator.
-    //
-    // If the iterator have an infinite length, this method won't return.
-    #[inline(always)]
-    fn last(&mut self) -> A {
-        let mut elm = match self.next() {
-            Some(x) => x,
-            None    => fail!("cannot get last element")
-        };
-        for self.advance |e| { elm = e; }
-        return elm;
+    fn last(&mut self) -> Option<A> {
+        let mut last = None;
+        for self.advance |x| { last = Some(x); }
+        last
     }
 
     /// Reduce an iterator to an accumulated value
@@ -203,7 +186,7 @@ impl<A, T: Iterator<A>> IteratorUtil<A> for T {
         return accum;
     }
 
-    /// Count the number of an iterator elemenrs
+    /// Count the number of items yielded by an iterator
     #[inline(always)]
     fn count(&mut self) -> uint { self.fold(0, |cnt, _x| cnt + 1) }
 
@@ -344,17 +327,13 @@ pub struct FilterMapIterator<'self, A, B, T> {
 impl<'self, A, B, T: Iterator<A>> Iterator<B> for FilterMapIterator<'self, A, B, T> {
     #[inline]
     fn next(&mut self) -> Option<B> {
-        loop {
-            match self.iter.next() {
-                None    => { return None; }
-                Some(a) => {
-                    match (self.f)(a) {
-                        Some(b) => { return Some(b); }
-                        None    => { loop; }
-                    }
-                }
+        for self.iter.advance |x| {
+            match (self.f)(x) {
+                Some(y) => return Some(y),
+                None => ()
             }
         }
+        None
     }
 }
 
@@ -579,7 +558,7 @@ mod tests {
 
     #[test]
     fn test_filter_map() {
-        let it  = Counter::new(0u, 1u).take(10)
+        let mut it = Counter::new(0u, 1u).take(10)
             .filter_map(|x: uint| if x.is_even() { Some(x*x) } else { None });
         assert_eq!(it.to_vec(), ~[0*0, 2*2, 4*4, 6*6, 8*8]);
     }
@@ -689,43 +668,15 @@ mod tests {
     fn test_iterator_nth() {
         let v = &[0, 1, 2, 3, 4];
         for uint::range(0, v.len()) |i| {
-            assert_eq!(v.iter().nth(i), &v[i]);
+            assert_eq!(v.iter().nth(i).unwrap(), &v[i]);
         }
     }
 
-    #[test]
-    #[should_fail]
-    fn test_iterator_nth_fail() {
-        let v = &[0, 1, 2, 3, 4];
-        v.iter().nth(5);
-    }
-
-    #[test]
-    fn test_iterator_first() {
-        let v = &[0, 1, 2, 3, 4];
-        assert_eq!(v.iter().first(), &0);
-        assert_eq!(v.slice(2, 5).iter().first(), &2);
-    }
-
-    #[test]
-    #[should_fail]
-    fn test_iterator_first_fail() {
-        let v: &[uint] = &[];
-        v.iter().first();
-    }
-
     #[test]
     fn test_iterator_last() {
         let v = &[0, 1, 2, 3, 4];
-        assert_eq!(v.iter().last(), &4);
-        assert_eq!(v.slice(0, 1).iter().last(), &0);
-    }
-
-    #[test]
-    #[should_fail]
-    fn test_iterator_last_fail() {
-        let v: &[uint] = &[];
-        v.iter().last();
+        assert_eq!(v.iter().last().unwrap(), &4);
+        assert_eq!(v.slice(0, 1).iter().last().unwrap(), &0);
     }
 
     #[test]