Commits on Feb 1, 2015

1. box: into_raw, from_raw functions …

   Functions are needed for safety and convenience.
   
   It is a common pattern to use `mem::transmute` to convert between
   `Box` and raw pointer, like this:
   
   ```
   let b = Box::new(3);
   let p = mem::transmute(b);
   // pass `p` to some C library
   ```
   
   After this commit, conversion can be written as:
   
   ```
   let p = boxed::into_raw(b);
   ```
   
   `into_raw` and `from_raw` functions are still unsafe, but they are
   much safer than `mem::transmute`, because *raw functions do not
   convert between incompatible pointers. For example, this likely
   incorrect code can be successfully compiled:
   
   ```
   let p: *mut u64 = ...
   let b: Box<u32> = mem::transmute(p);
   ```
   
   Using `from_raw` results in compile-time error:
   
   ```
   let p: *mut u64 = ...
   let b: Box<u32> = Box::from_raw(p); // compile-time error
   ```
   
   `into_raw` and `from_raw` functions are similar to C++ `std::unique_ptr`
   `release` function [1] and constructor from pointer [2].
   
   [1] http://en.cppreference.com/w/cpp/memory/unique_ptr/release
   [2] http://en.cppreference.com/w/cpp/memory/unique_ptr/unique_ptr

   

   stepancheg committed Feb 1, 2015
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