Allow T op= &T for built-in numeric types T

Currently, there are 4 ways to add two i32's together: a + b, a + &b,
&a + b and &a + &b. The same is possible for all other binary operators
and for all built-in numeric types that support those binary operators.
Similarly, unary operators also have both a ref and a non-ref version,
e.g., -7 == -&7.

However, the assignment versions of these binary operators don't allow
a ref right-hand side. This commit fixes that inconsistency by
implementing these operators.

These changes should be fully backwards compatible.

Author: michiel-de-muynck

src/libcore/internal_macros.rs

@@ -68,3 +68,21 @@ macro_rules! forward_ref_binop {
         }
     }
 }
+
+// implements "T op= &U", based on "T op= U"
+// where U is expected to be `Copy`able
+macro_rules! forward_ref_op_assign {
+    (impl $imp:ident, $method:ident for $t:ty, $u:ty) => {
+        forward_ref_op_assign!(impl $imp, $method for $t, $u,
+                #[stable(feature = "op_assign_builtins_by_ref", since = "1.18.0")]);
+    };
+    (impl $imp:ident, $method:ident for $t:ty, $u:ty, #[$attr:meta]) => {
+        #[$attr]
+        impl<'a> $imp<&'a $u> for $t {
+            #[inline]
+            fn $method(&mut self, other: &'a $u) {
+                $imp::$method(self, *other);
+            }
+        }
+    }
+}

src/libcore/ops.rs

@@ -1346,6 +1346,8 @@ macro_rules! add_assign_impl {
             #[rustc_inherit_overflow_checks]
             fn add_assign(&mut self, other: $t) { *self += other }
         }
+
+        forward_ref_op_assign! { impl AddAssign, add_assign for $t, $t }
     )+)
 }
 
@@ -1403,6 +1405,8 @@ macro_rules! sub_assign_impl {
             #[rustc_inherit_overflow_checks]
             fn sub_assign(&mut self, other: $t) { *self -= other }
         }
+
+        forward_ref_op_assign! { impl SubAssign, sub_assign for $t, $t }
     )+)
 }
 
@@ -1449,6 +1453,8 @@ macro_rules! mul_assign_impl {
             #[rustc_inherit_overflow_checks]
             fn mul_assign(&mut self, other: $t) { *self *= other }
         }
+
+        forward_ref_op_assign! { impl MulAssign, mul_assign for $t, $t }
     )+)
 }
 
@@ -1494,6 +1500,8 @@ macro_rules! div_assign_impl {
             #[inline]
             fn div_assign(&mut self, other: $t) { *self /= other }
         }
+
+        forward_ref_op_assign! { impl DivAssign, div_assign for $t, $t }
     )+)
 }
 
@@ -1539,6 +1547,8 @@ macro_rules! rem_assign_impl {
             #[inline]
             fn rem_assign(&mut self, other: $t) { *self %= other }
         }
+
+        forward_ref_op_assign! { impl RemAssign, rem_assign for $t, $t }
     )+)
 }
 
@@ -1626,6 +1636,8 @@ macro_rules! bitand_assign_impl {
             #[inline]
             fn bitand_assign(&mut self, other: $t) { *self &= other }
         }
+
+        forward_ref_op_assign! { impl BitAndAssign, bitand_assign for $t, $t }
     )+)
 }
 
@@ -1671,6 +1683,8 @@ macro_rules! bitor_assign_impl {
             #[inline]
             fn bitor_assign(&mut self, other: $t) { *self |= other }
         }
+
+        forward_ref_op_assign! { impl BitOrAssign, bitor_assign for $t, $t }
     )+)
 }
 
@@ -1716,6 +1730,8 @@ macro_rules! bitxor_assign_impl {
             #[inline]
             fn bitxor_assign(&mut self, other: $t) { *self ^= other }
         }
+
+        forward_ref_op_assign! { impl BitXorAssign, bitxor_assign for $t, $t }
     )+)
 }
 
@@ -1764,6 +1780,8 @@ macro_rules! shl_assign_impl {
                 *self <<= other
             }
         }
+
+        forward_ref_op_assign! { impl ShlAssign, shl_assign for $t, $f }
     )
 }
 
@@ -1830,6 +1848,8 @@ macro_rules! shr_assign_impl {
                 *self >>= other
             }
         }
+
+        forward_ref_op_assign! { impl ShrAssign, shr_assign for $t, $f }
     )
 }