All,
The documentation for swift4 shows the following are still valid
&+&-&*when I convert my swift 3 code
public extension Integer
{
var lowbit: Self { return self & (~self &+ 1) }
var isPower2 : Bool { return 0 < self && self & (self &- 1) == 0 }
}I get the following errors
Binary operator '&+' cannot be applied to operands of type 'Self' and 'Int'Did I miss something in the release notes?
Thanks for the help.
>> Did I miss something in the release notes?
Actually, yes, you did. The release notes (https://developer.apple.com/library/content/releasenotes/DeveloperTools/RN-Xcode/Chapters/Introduction.html) say this:
A new family of integer protocols enables more generic algorithms:
• Numeric, types that support arithmetic operators
• BinaryInteger, integer types that have a binary representation and support bitwise operations
• FixedWidthInteger, integer types that use a fixed size and support the concept of arithmetic operations that report overflow
As Claude pointed out, the old "Integer" protocol has been renamed, but the overflow-reporting operators were moved to a new protocol, FixedWidthInteger (because overflow only fully makes sense for integers with a fixed width representation). That means the correct "fix" is along these lines:
public extension FixedWidthInteger
{
var lowbit: Self { return self & (~self &+ 1) }
}You can read up on all the gory details in SE-104 (github.com/apple/swift-evolution/blob/master/proposals/0104-improved-integers.md).
When I try in XCode 9.2 (Swift4), I get 2 errors :
Integer has been renamed BinaryInteger
And the same error as yours
If I replace the definition of extension by
public extension UInt32
{
var lowbit: UInt32 { return self & (~self &+ 1) }
}no more error
Seems that &+ works with unsigned only
>> Did I miss something in the release notes?
Actually, yes, you did. The release notes (https://developer.apple.com/library/content/releasenotes/DeveloperTools/RN-Xcode/Chapters/Introduction.html) say this:
A new family of integer protocols enables more generic algorithms:
• Numeric, types that support arithmetic operators
• BinaryInteger, integer types that have a binary representation and support bitwise operations
• FixedWidthInteger, integer types that use a fixed size and support the concept of arithmetic operations that report overflow
As Claude pointed out, the old "Integer" protocol has been renamed, but the overflow-reporting operators were moved to a new protocol, FixedWidthInteger (because overflow only fully makes sense for integers with a fixed width representation). That means the correct "fix" is along these lines:
public extension FixedWidthInteger
{
var lowbit: Self { return self & (~self &+ 1) }
}You can read up on all the gory details in SE-104 (github.com/apple/swift-evolution/blob/master/proposals/0104-improved-integers.md).
Great thank you.