> On Oct 18, 2016, at 12:17 PM, Guoye Zhang via swift-evolution > <swift-evolution@swift.org> wrote: > I propose to ban the top value in Int/UInt which is 0xFFFF... in hex. Int > family would lose its smallest value, and UInt family would lose its largest > value. Top value is reserved for nil in optionals. An additional benefit is > that negating an Int would never crash.
There are two ways to do this (using Int8 for example) 1. 0xFF reserved to mean nil. As this normally means -1, all negative numbers now use complements rather than two’s complement form. This breaks a lot of binary math. 2. 0x80 reserved to mean nil. This is normally -128. Overflow would have to be modified in order to support this (otherwise, 127 + 1 == nil). bit padding no longer works (0x80 would expand to 0xFF80 for a Int16 with bit padding, not 0x8000) > > Interacting with C/Obj-C is a major concern, but since we are already > importing some of the unsigned integers as Int which loses half the values, > one value is not such big a drawback. Alternatively, we could leave current > behavior as CInt/CUInt. Converting them to the new Int?/UInt? doesn't > generate any instructions since the invalid value already represents nil. > As the appropriate integer minimum value may already be in use in C or Objective C code, I believe you would need to define a new integer types to support this sort of constrained type. Where I would see something like this be most appropriate would be for supporting a “BigNumber” type in the language, preferably as the default integer type. Ruby does this for example with Fixnum/Bignum - all values in Ruby are actually tagged pointers (where the lower bits are set to cause invalid alignment of a pointer in order to indicate it is a special case immediate value). So if the lowest bit is set, the value is a FixNum integer with a lower max/higher min than a traditional integer. On overflow, the value is promoted to be a BigNum, which is a reference to an arbitrary sized integer on the heap. -DW _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
