rearrange the os::{Stack, StackSource} code a little

src/os.rs

@@ -6,6 +6,8 @@ use stack;
 #[cfg(unix)]
 #[path = "os/unix.rs"] mod sys;
 
+pub struct StackSource;
+
 #[allow(raw_pointer_derive)]
 #[derive(Debug)]
 pub struct Stack {
@@ -13,33 +15,11 @@ pub struct Stack {
   len: usize
 }
 
-pub struct StackSource;
-
 impl stack::StackSource for StackSource {
   type Output = Stack;
   type Error = IoError;
 
   fn get_stack(size: usize) -> Result<Stack, IoError> {
-    Stack::new(size)
-  }
-}
-
-impl stack::Stack for Stack {
-  fn top(&mut self) -> *mut u8 {
-    unsafe {
-      self.ptr.offset(self.len as isize)
-    }
-  }
-
-  fn limit(&self) -> *const u8 {
-    unsafe {
-      self.ptr.offset(sys::page_size() as isize)
-    }
-  }
-}
-
-impl Stack {
-  fn new(size: usize) -> Result<Stack, IoError> {
     let page_size = sys::page_size();
 
     // round the page size up,
@@ -64,6 +44,20 @@ impl Stack {
   }
 }
 
+impl stack::Stack for Stack {
+  fn top(&mut self) -> *mut u8 {
+    unsafe {
+      self.ptr.offset(self.len as isize)
+    }
+  }
+
+  fn limit(&self) -> *const u8 {
+    unsafe {
+      self.ptr.offset(sys::page_size() as isize)
+    }
+  }
+}
+
 impl Drop for Stack {
   fn drop(&mut self) {
     unsafe {