# &-=(_:_:)

Subtracts the second value from the first and stores the difference in the left-hand-side variable, wrapping any overflow.

Available because

`Self`

conforms to`FixedWidthInteger`

.

`static func &-= (lhs: inout Self, rhs: Self)`

## Parameters

- lhs
A numeric value.

- rhs
The value to subtract from

`lhs`

.

## Overview

The masking subtraction assignment operator (`&-=`

) silently wraps any overflow that occurs during the operation. In the following example, the difference of `10`

and `21`

is less than zero, the minimum representable `UInt`

value, so the result is the result is the partial value after discarding the overflowing bits.

```
var x: Int8 = 21
x &-= 10
// x == 11
var y: UInt8 = 10
y &-= 21
// y == 245 (after overflow)
```

For more about arithmetic with overflow operators, see Overflow Operators in *The Swift Programming Language*.