[swift-evolution] [Pitch] `Int.init(ObjectIdentifier)` and `UInt.init(ObjectIdentifier)` should have a `bitPattern:` label
David Sweeris
davesweeris at mac.com
Fri Jul 15 14:32:53 CDT 2016
+1
Sent from my iPhone
> On Jul 13, 2016, at 18:39, Arnold Schwaighofer via swift-evolution <swift-evolution at swift.org> wrote:
>
> Int.init(ObjectIdentifier) and UInt.init(ObjectIdentifier) should have a 'bitPattern:’ label to make it clear at the use site that we interpret the value as a bit pattern.
>
> In Swift we have ObjectIdentifier values which uniquely identify a class instance or metatype. They are implemented as a struct which holds the value of the reference to the instance or metatype as a raw pointer.
>
> /// A unique identifier for a class instance or metatype.
> public struct ObjectIdentifier : Hashable, Comparable {
> internal let _value: Builtin.RawPointer
> ...
> }
>
>
> We have constructors for Int and Uint that capture this value. These constructors don’t have an argument label.
>
> extension UInt {
> /// Create a `UInt` that captures the full value of `objectID`.
> public init(_ objectID: ObjectIdentifier) {
> self.init(Builtin.ptrtoint_Word(objectID._value))
> }
> }
>
> extension Int {
> /// Create an `Int` that captures the full value of `objectID`.
> public init(_ objectID: ObjectIdentifier) {
> self.init(bitPattern: UInt(objectID))
> }
> }
>
> This proposals suggest adding a label ‘bitPattern’ to the constructor: Int.init(bitPattern: ObjectIdentifier).
>
> extension UInt {
> /// Create a `UInt` that captures the full value of `objectID`.
> public init(bitPattern objectID: ObjectIdentifier) {
> self.init(Builtin.ptrtoint_Word(objectID._value))
> }
> }
>
> extension Int {
> /// Create an `Int` that captures the full value of `objectID`.
> public init(bitPattern objectID: ObjectIdentifier) {
> self.init(bitPattern: UInt(objectID))
> }
> }
>
>
> Motivation
> ==========
>
> Adding a label ‘bitPattern’ to the constructors makes it clear that we interpret the pointer value as a bit pattern at the use site. It is similar to what we do in other APIs, for example in "UInt(bitPattern: UnsafePointer<Void>(value)))"
>
> Impact on existing code
> =======================
>
> Existing code will have to add the bitPattern label.
>
>
> Alternatives
> ============
>
> Leave as is.
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
More information about the swift-evolution
mailing list