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[SR-7868] Data and DispatchData have subtly different signatures for enumerateBytes #652

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Lukasa opened this issue Jun 4, 2018 · 2 comments
Open

[SR-7868] Data and DispatchData have subtly different signatures for enumerateBytes #652

Lukasa opened this issue Jun 4, 2018 · 2 comments
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bug Foundation libdispatch

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@Lukasa
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Lukasa commented Jun 4, 2018

Previous ID SR-7868
Radar rdar://problem/40775762
Original Reporter @Lukasa
Type Bug
Environment

Swift 4.2 beta

Additional Detail from JIRA
Votes 0
Component/s Foundation, libdispatch
Labels Bug
Assignee None
Priority Medium

md5: 7f82935997669109761a47ee765077b8

Issue Description:

While attempting to write a protocol for both Data and DispatchData that covers their shared `enumerateBytes` method, I discovered that it is not really possible to do that. Consider the following example program:

import struct Foundation.Data
import struct Dispatch.DispatchData

protocol ByteEnumerator: Collection {
    func enumerateBytes(block: (UnsafeBufferPointer<UInt8>, Self.Index, inout Bool) -> Void)
}

extension Data: ByteEnumerator { }
extension DispatchData: ByteEnumerator { }

This does not compile, because Data has no label on its block:

test.swift:8:1: error: method 'enumerateBytes' has different argument labels from those required by protocol 'ByteEnumerator' ('enumerateBytes(block:)')
extension Data: ByteEnumerator { }
^
Foundation.Data:40:17: note: 'enumerateBytes' declared here
    public func enumerateBytes(_ block: (UnsafeBufferPointer<UInt8>, Data.Index, inout Bool) -> Void)
                ^
test.swift:5:10: note: requirement 'enumerateBytes(block:)' declared here
    func enumerateBytes(block: (UnsafeBufferPointer<UInt8>, Self.Index, inout Bool) -> Void)

If you try to suppress the label by changing the protocol method from func enumerateBytes(block: (UnsafeBufferPointer<UInt8>, Self.Index, inout Bool) -> Void) to func enumerateBytes(_ block: (UnsafeBufferPointer<UInt8>, Self.Index, inout Bool) -> Void), this will again fail to compile, this time because of DispatchData:

test.swift:9:1: error: method 'enumerateBytes(block:)' has different argument labels from those required by protocol 'ByteEnumerator' ('enumerateBytes')
extension DispatchData: ByteEnumerator { }
^
Dispatch.DispatchData:19:17: note: 'enumerateBytes(block:)' declared here
    public func enumerateBytes(block: (UnsafeBufferPointer<UInt8>, Int, inout Bool) -> Void)
                ^
test.swift:5:10: note: requirement 'enumerateBytes' declared here
    func enumerateBytes(_ block: (UnsafeBufferPointer<UInt8>, Self.Index, inout Bool) -> Void)

Given that these two data types can be bridged on Darwin, but not Linux, this inconsistency should probably be remedied.

(As a post-script, a tempting approach to bridge over this would be for my protocol to provide a default implementation for one case in terms of the other. However, because of the tail-closure syntax, doing this would cause an enormous number of compile errors.)
@Lukasa
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Lukasa commented Jun 4, 2018

@swift-ci create

@Lukasa
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Lukasa commented Jun 4, 2018

I should note that this affects both Darwin and Linux identically.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@shahmishal shahmishal transferred this issue from apple/swift May 5, 2022
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@Lukasa