[swift-evolution] Shift operator: the type of the second operand

[Greg Titus]

+1. In fact, I would go even farther than asking for an additional version that uses Int on the rhs, I think all of the existing definitions are arguably wrong and they should all just be changed to use Int. I just took a brief scan of all uses of >> and << in the stdlib: most use constants on the rhs, and so would be unaffected. It looks like all the rest either use Int on the lhs or require explicit casting or calling numericCast() to get the rhs to match. 

	- Greg

> On Dec 18, 2015, at 3:55 AM, Jeremy Pereira via swift-evolution <swift-evolution at swift.org> wrote:
> 
> These are the definitions of the right shift operators
> 
> 	public func >>(lhs: Int8, rhs: Int8) -> Int8
> 
> 	public func >>(lhs: Int, rhs: Int) -> Int
> 
> 	public func >>(lhs: UInt, rhs: UInt) -> UInt
> 
> 	public func >>(lhs: Int64, rhs: Int64) -> Int64
> 
> 	public func >>(lhs: UInt64, rhs: UInt64) -> UInt64
> 
> 	public func >>(lhs: UInt8, rhs: UInt8) -> UInt8
> 
> 	public func >>(lhs: UInt16, rhs: UInt16) -> UInt16
> 
> 	public func >>(lhs: Int16, rhs: Int16) -> Int16
> 
> 	public func >>(lhs: Int32, rhs: Int32) -> Int32
> 
> 	public func >>(lhs: UInt32, rhs: UInt32) -> UInt32
> 
> 
> Note that both left and right hand side are of the same type. In my opinion, rhs, which represents the number of bits to shift, should always be an Int e.g.
> 
> 	public func >>(lhs: UInt64, rhs: Int) -> UInt64
> 
> The two operands are fundamentally different, the left hand one is conceptually an array of bits and the right hand one is conceptually a count. 
> 
> The current definitions mean that I almost always have to do a cast on the right operand with shift operations. e.g. the following snippet that converts a UInt64 into an array of boolean values.
> 
>    let aNumber: UInt64 = 0x123456
>    var numberAsBits: [Bool] = [];
>    for i in 0 ..< 64
>    {
>        numberAsBits.append((aNumber >> i) & 1 != 0); // Error because i needs to be cast to a UInt64
>    }
> 
> I would like additional versions of the shift operator where rhs is an Int please.
> 
> Needless to say, the same applies to the left shift operators.
> 
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