auto merge of #8183 : omasanori/rust/migrate-new, r=sanxiyn

It seems that relatively new code uses `Foo::new()` instead of `Foo()` so I wrote a patch to migrate some structs to the former style.
Is it a right direction? If there are any guidelines not to use new()-style, could you add them to the [style guide](https://github.com/omasanori/rust/wiki/Note-style-guide)?

Author: bors

src/libextra/arena.rs

@@ -67,17 +67,16 @@ pub struct Arena {
     priv chunks: @mut MutList<Chunk>,
 }
 
-#[unsafe_destructor]
-impl Drop for Arena {
-    fn drop(&self) {
-        unsafe {
-            destroy_chunk(&self.head);
-            do self.chunks.each |chunk| {
-                if !chunk.is_pod {
-                    destroy_chunk(chunk);
-                }
-                true
-            };
+impl Arena {
+    pub fn new() -> Arena {
+        Arena::new_with_size(32u)
+    }
+
+    pub fn new_with_size(initial_size: uint) -> Arena {
+        Arena {
+            head: chunk(initial_size, false),
+            pod_head: chunk(initial_size, true),
+            chunks: @mut MutNil,
         }
     }
 }
@@ -92,18 +91,21 @@ fn chunk(size: uint, is_pod: bool) -> Chunk {
     }
 }
 
-pub fn arena_with_size(initial_size: uint) -> Arena {
-    Arena {
-        head: chunk(initial_size, false),
-        pod_head: chunk(initial_size, true),
-        chunks: @mut MutNil,
+#[unsafe_destructor]
+impl Drop for Arena {
+    fn drop(&self) {
+        unsafe {
+            destroy_chunk(&self.head);
+            do self.chunks.each |chunk| {
+                if !chunk.is_pod {
+                    destroy_chunk(chunk);
+                }
+                true
+            };
+        }
     }
 }
 
-pub fn Arena() -> Arena {
-    arena_with_size(32u)
-}
-
 #[inline]
 fn round_up_to(base: uint, align: uint) -> uint {
     (base + (align - 1)) & !(align - 1)
@@ -276,7 +278,7 @@ impl Arena {
 
 #[test]
 fn test_arena_destructors() {
-    let arena = Arena();
+    let arena = Arena::new();
     for i in range(0u, 10) {
         // Arena allocate something with drop glue to make sure it
         // doesn't leak.
@@ -291,7 +293,7 @@ fn test_arena_destructors() {
 #[should_fail]
 #[ignore(cfg(windows))]
 fn test_arena_destructors_fail() {
-    let arena = Arena();
+    let arena = Arena::new();
     // Put some stuff in the arena.
     for i in range(0u, 10) {
         // Arena allocate something with drop glue to make sure it

src/test/bench/shootout-binarytrees.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 extern mod extra;
-use extra::arena;
+use extra::arena::Arena;
 
 enum Tree<'self> {
     Nil,
@@ -25,7 +25,7 @@ fn item_check(t: &Tree) -> int {
     }
 }
 
-fn bottom_up_tree<'r>(arena: &'r arena::Arena, item: int, depth: int)
+fn bottom_up_tree<'r>(arena: &'r Arena, item: int, depth: int)
                    -> &'r Tree<'r> {
     if depth > 0 {
         return arena.alloc(
@@ -57,15 +57,15 @@ fn main() {
         max_depth = n;
     }
 
-    let stretch_arena = arena::Arena();
+    let stretch_arena = Arena::new();
     let stretch_depth = max_depth + 1;
     let stretch_tree = bottom_up_tree(&stretch_arena, 0, stretch_depth);
 
     printfln!("stretch tree of depth %d\t check: %d",
               stretch_depth,
               item_check(stretch_tree));
 
-    let long_lived_arena = arena::Arena();
+    let long_lived_arena = Arena::new();
     let long_lived_tree = bottom_up_tree(&long_lived_arena, 0, max_depth);
     let mut depth = min_depth;
     while depth <= max_depth {

src/test/run-pass/placement-new-arena.rs

@@ -11,10 +11,10 @@
 // except according to those terms.
 
 extern mod extra;
-use extra::arena;
+use extra::arena::Arena;
 
 pub fn main() {
-    let mut arena = arena::Arena();
+    let mut arena = Arena::new();
     let p = &mut arena;
     let x = p.alloc(|| 4u);
     printf!("%u", *x);