core: Remove the cast module

This commit revisits the `cast` module in libcore and libstd, and scrutinizes
all functions inside of it. The result was to remove the `cast` module entirely,
folding all functionality into the `mem` module. Specifically, this is the fate
of each function in the `cast` module.

* transmute - This function was moved to `mem`, but it is now marked as
              #[unstable]. This is due to planned changes to the `transmute`
              function and how it can be invoked (see the #[unstable] comment).
              For more information, see RFC 5 and #12898

* transmute_copy - This function was moved to `mem`, with clarification that is
                   is not an error to invoke it with T/U that are different
                   sizes, but rather that it is strongly discouraged. This
                   function is now #[stable]

* forget - This function was moved to `mem` and marked #[stable]

* bump_box_refcount - This function was removed due to the deprecation of
                      managed boxes as well as its questionable utility.

* transmute_mut - This function was previously deprecated, and removed as part
                  of this commit.

* transmute_mut_unsafe - This function doesn't serve much of a purpose when it
                         can be achieved with an `as` in safe code, so it was
                         removed.

* transmute_lifetime - This function was removed because it is likely a strong
                       indication that code is incorrect in the first place.

* transmute_mut_lifetime - This function was removed for the same reasons as
                           `transmute_lifetime`

* copy_lifetime - This function was moved to `mem`, but it is marked
                  `#[unstable]` now due to the likelihood of being removed in
                  the future if it is found to not be very useful.

* copy_mut_lifetime - This function was also moved to `mem`, but had the same
                      treatment as `copy_lifetime`.

* copy_lifetime_vec - This function was removed because it is not used today,
                      and its existence is not necessary with DST
                      (copy_lifetime will suffice).

In summary, the cast module was stripped down to these functions, and then the
functions were moved to the `mem` module.

    transmute - #[unstable]
    transmute_copy - #[stable]
    forget - #[stable]
    copy_lifetime - #[unstable]
    copy_mut_lifetime - #[unstable]

[breaking-change]

1 files changed, 5 insertions, 5 deletions

diff --git a/src/libstd/num/f32.rs b/src/libstd/num/f32.rs
index ea248b6d40d..29c206b32fc 100644
--- a/src/libstd/num/f32.rs
+++ b/src/libstd/num/f32.rs
@@ -15,13 +15,13 @@
 
 use prelude::*;
 
-use cast;
 use from_str::FromStr;
+use intrinsics;
 use libc::c_int;
-use num::{FPCategory, FPNaN, FPInfinite , FPZero, FPSubnormal, FPNormal};
+use mem;
 use num::strconv;
+use num::{FPCategory, FPNaN, FPInfinite , FPZero, FPSubnormal, FPNormal};
 use num;
-use intrinsics;
 
 pub use core::f32::{RADIX, MANTISSA_DIGITS, DIGITS, EPSILON, MIN_VALUE};
 pub use core::f32::{MIN_POS_VALUE, MAX_VALUE, MIN_EXP, MAX_EXP, MIN_10_EXP};
@@ -111,7 +111,7 @@ impl Float for f32 {
         static EXP_MASK: u32 = 0x7f800000;
         static MAN_MASK: u32 = 0x007fffff;
 
-        let bits: u32 = unsafe { cast::transmute(self) };
+        let bits: u32 = unsafe { mem::transmute(self) };
         match (bits & MAN_MASK, bits & EXP_MASK) {
             (0, 0)        => FPZero,
             (_, 0)        => FPSubnormal,
@@ -168,7 +168,7 @@ impl Float for f32 {
 
     /// Returns the mantissa, exponent and sign as integers.
     fn integer_decode(self) -> (u64, i16, i8) {
-        let bits: u32 = unsafe { cast::transmute(self) };
+        let bits: u32 = unsafe { mem::transmute(self) };
         let sign: i8 = if bits >> 31 == 0 { 1 } else { -1 };
         let mut exponent: i16 = ((bits >> 23) & 0xff) as i16;
         let mantissa = if exponent == 0 {