Fold collections debug impls

Also convert [T]'s Debug impl. The behavior of the alternate flag here's
changing.

src/libcollections/btree/map.rs

@@ -904,11 +904,7 @@ fn cmp(&self, other: &BTreeMap<K, V>) -> Ordering {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K: Debug, V: Debug> Debug for BTreeMap<K, V> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let mut builder = f.debug_map();
-        for (k, v) in self {
-            builder = builder.entry(k, v);
-        }
-        builder.finish()
+        self.iter().fold(f.debug_map(), |b, (k, v)| b.entry(k, v)).finish()
     }
 }
 

src/libcollections/btree/set.rs

@@ -628,11 +628,7 @@ fn bitor(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Debug> Debug for BTreeSet<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let mut builder = f.debug_set();
-        for x in self {
-            builder = builder.entry(x);
-        }
-        builder.finish()
+        self.iter().fold(f.debug_set(), |b, e| b.entry(e)).finish()
     }
 }
 

src/libcollections/linked_list.rs

@@ -927,11 +927,7 @@ fn clone(&self) -> LinkedList<A> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<A: fmt::Debug> fmt::Debug for LinkedList<A> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let mut builder = f.debug_list();
-        for e in self {
-            builder = builder.entry(e);
-        }
-        builder.finish()
+        self.iter().fold(f.debug_list(), |b, e| b.entry(e)).finish()
     }
 }
 

src/libcore/fmt/mod.rs

@@ -1017,22 +1017,7 @@ fn fmt(&self, f: &mut Formatter) -> Result { f.pad("&Any") }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Debug> Debug for [T] {
     fn fmt(&self, f: &mut Formatter) -> Result {
-        if f.flags & (1 << (FlagV1::Alternate as u32)) == 0 {
-            try!(write!(f, "["));
-        }
-        let mut is_first = true;
-        for x in self {
-            if is_first {
-                is_first = false;
-            } else {
-                try!(write!(f, ", "));
-            }
-            try!(write!(f, "{:?}", *x))
-        }
-        if f.flags & (1 << (FlagV1::Alternate as u32)) == 0 {
-            try!(write!(f, "]"));
-        }
-        Ok(())
+        self.iter().fold(f.debug_list(), |b, e| b.entry(e)).finish()
     }
 }
 

src/libstd/collections/hash/map.rs

@@ -1226,11 +1226,7 @@ impl<K, V, S> Debug for HashMap<K, V, S>
     where K: Eq + Hash + Debug, V: Debug, S: HashState
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let mut builder = f.debug_map();
-        for (k, v) in self.iter() {
-            builder = builder.entry(k, v);
-        }
-        builder.finish()
+        self.iter().fold(f.debug_map(), |b, (k, v)| b.entry(k, v)).finish()
     }
 }
 

src/libstd/collections/hash/set.rs

@@ -614,11 +614,7 @@ impl<T, S> fmt::Debug for HashSet<T, S>
           S: HashState
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let mut builder = f.debug_set();
-        for x in self {
-            builder = builder.entry(x);
-        }
-        builder.finish()
+        self.iter().fold(f.debug_set(), |b, e| b.entry(e)).finish()
     }
 }