---
title: "SE-0124: `Int.init(ObjectIdentifier)` and `UInt.init(ObjectIdentifier)` should have a `bitPattern:` label"
framework: swift-evolution
role: article
path: swift-evolution/0124-bitpattern-label-for-int-initializer-objectidentfier
---

# SE-0124: `Int.init(ObjectIdentifier)` and `UInt.init(ObjectIdentifier)` should have a `bitPattern:` label

* Proposal: [SE-0124](0124-bitpattern-label-for-int-initializer-objectidentfier.md)
* Author: [Arnold Schwaighofer](https://github.com/aschwaighofer)
* Review Manager: [Chris Lattner](https://github.com/lattner)
* Status: **Implemented (Swift 3.0)**
* Decision Notes: [Rationale](https://forums.swift.org/t/accepted-se-0124-int-init-objectidentifier-and-uint-init-objectidentifier-should-have-a-bitpattern-label/3474)
* Bug: [SR-2064](https://bugs.swift.org/browse/SR-2064)

## Introduction

`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.

```swift   public func <(lhs: ObjectIdentifier, rhs: ObjectIdentifier) -> Bool {     return UInt(bitPattern: lhs) < UInt(bitPattern: rhs)   } ```

- Swift-evolution thread: [Pitch](https://forums.swift.org/t/pitch-int-init-objectidentifier-and-uint-init-objectidentifier-should-have-a-bitpattern-label/3384) - Swift Bug: [SR-2064](https://bugs.swift.org/browse/SR-2064) - Branch with change to stdlib: [int_init_objectidentifier_label] (https://github.com/aschwaighofer/swift/tree/int_init_objectidentifier_label)

## Motivation

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.

```swift   /// 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.

```swift   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.

```swift   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))     }   } ```

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)))`.

## Proposed solution

See above.

## Detailed design

We will change the initializers of `Int` and `UInt` as shown above. The compiler will suggest corrections in existing code because we mark the old API unavailable.

## Impact on existing code

Existing code will have to add the argument label.

## Alternatives considered

Leave as is. The API will be inconsistent with other APIs such as the `UInt(bitPattern: UnsafePointer<T>)` API.