[SR-1811] Swift 3 regression related to inout closure params and protocols #44420

jepers · 2016-06-18T00:34:19Z


Previous ID	SR-1811
Radar	rdar://problem/26902750
Original Reporter	@jepers
Type	Bug
Status	Closed
Resolution	Duplicate

Environment

OS X 10.11.5 (15F34), Xcode 8.0 beta (8S128d), Xcode 7.3.1

Additional Detail from JIRA


Votes	0
Component/s	Compiler
Labels	Bug, 3.0Regression, TypeChecker
Assignee	None
Priority	Medium

md5: 102c68ad72df56e90c563afcc1ec867c

duplicates:

SR-3479 Segmentation fault and other error for closure with inout parameter

Issue Description:

Below is the same short program in two versions, one for Swift 3 (Xcode 8 beta) and the other for Swift 2.2 (Xcode 7.3.1).

The version for Swift 3 demonstrates a compiler bug that I'm pretty sure was resolved a "long" time ago. I can't find the bug report right now but I might try to find it again later.

Bug/regression-demonstrating Swift 3 version (Xcode 8.0 beta (8S128d)):

struct PxBGRAsRGB {
    var b, g, r, a : UInt8
}
protocol RasterProtocol: class {
    associatedtype Pixel
    var width: Int { get }
    var height: Int { get }
    var rowBytes: Int { get }
    var data: UnsafeMutablePointer<UInt8> { get }
    subscript(x: Int, y: Int) -> Pixel { get set }
}
extension RasterProtocol {
    subscript(x: Int, y: Int) -> Pixel {
        get {
            precondition(x >= 0 && y >= 0 && x < width && y < height)
            return UnsafePointer<Pixel>(data.advanced(by: x * strideof(Pixel) + y * rowBytes)).pointee
        }
        set {
            precondition(x >= 0 && y >= 0 && x < width && y < height)
            UnsafeMutablePointer<Pixel>(data.advanced(by: x * strideof(Pixel) + y * rowBytes)).pointee = newValue
        }
    }
    func withEachPixel(inPlacePixelOp: @noescape (p: inout Pixel) -> Void) {
        for y in 0 ..< height { for x in 0 ..< width { inPlacePixelOp(p: &self[x, y]) } }
    }
}
final class Raster<P> : NonObjectiveCBase, RasterProtocol {
    typealias Pixel = P
    let width: Int
    let height: Int
    let rowBytes: Int
    let data: UnsafeMutablePointer<UInt8>
    init(width: Int, height: Int, rowBytes: Int) {
        precondition(width > 0 && height > 0 && rowBytes >= strideof(Pixel) * width)
        self.width = width
        self.height = height
        self.rowBytes = rowBytes
        data = UnsafeMutablePointer<UInt8>.init(allocatingCapacity: rowBytes * height)
    }
    deinit { data.deallocateCapacity(rowBytes * height) }
    func withEachPixel_2(inPlacePixelOp: @noescape (p: inout Pixel) -> Void) {
        for y in 0 ..< height { for x in 0 ..< width { inPlacePixelOp(p: &self[x, y]) } }
    }
}
let r = Raster<PxBGRAsRGB>.init(width: 240, height: 320, rowBytes: 240 * 4)
// Swift 3 regression? (Corresponding code worked in Xcode 7.3.1, Swift 2.2)
// r.withEachPixel { $0.a = 255 } // Error: Expression of type '()' is ambigous without more context
// r.withEachPixel { (p) in p.a = 255 } // Error: Expression of type '()' is ambigous without more context
//
// Workarounds for Swift 3, Xcode 8.0 beta (8S128d):
r.withEachPixel { (p: inout PxBGRAsRGB) in p.a = 255 } // OK
r.withEachPixel_2 { $0.a = 255 } // Also OK (when the method is declared in Raster instead of in RasterProtocol)

Working Swift 2.2 version for comparison:

struct PxBGRAsRGB {
    var b, g, r, a : UInt8
}
protocol RasterProtocol: class {
    associatedtype Pixel
    var width: Int { get }
    var height: Int { get }
    var rowBytes: Int { get }
    var data: UnsafeMutablePointer<UInt8> { get }
    subscript(x: Int, y: Int) -> Pixel { get set }
}
extension RasterProtocol {
    subscript(x: Int, y: Int) -> Pixel {
        get {
            precondition(x >= 0 && y >= 0 && x < width && y < height)
            return UnsafePointer<Pixel>(data.advancedBy(x * strideof(Pixel) + y * rowBytes)).memory
        }
        set {
            precondition(x >= 0 && y >= 0 && x < width && y < height)
            UnsafeMutablePointer<Pixel>(data.advancedBy(x * strideof(Pixel) + y * rowBytes)).memory = newValue
        }
    }
    func withEachPixel(@noescape inPlacePixelOp: (p: inout Pixel) -> Void) {
        for y in 0 ..< height { for x in 0 ..< width { inPlacePixelOp(p: &self[x, y]) } }
    }
}
final class Raster<P> : NonObjectiveCBase, RasterProtocol {
    typealias Pixel = P
    let width: Int
    let height: Int
    let rowBytes: Int
    let data: UnsafeMutablePointer<UInt8>
    init(width: Int, height: Int, rowBytes: Int) {
        precondition(width > 0 && height > 0 && rowBytes >= strideof(Pixel) * width)
        self.width = width
        self.height = height
        self.rowBytes = rowBytes
        data = UnsafeMutablePointer<UInt8>.alloc(rowBytes * height)
    }
    deinit { data.dealloc(rowBytes * height) }
}
let r = Raster<PxBGRAsRGB>.init(width: 240, height: 320, rowBytes: 240 * 4)
// This evidently works in Swift 2.2 (Xcode 7.3.1):
r.withEachPixel { $0.a = 255 } // OK
r.withEachPixel { (p) in p.a = 255 } // OK

The text was updated successfully, but these errors were encountered:

belkadan · 2016-06-20T19:44:45Z

Huh. I didn't remember this ever working reliably.

jepers · 2016-07-19T21:09:17Z

It (the short form) does work correctly in Xcode 7.3.1, Swift 2.2, and having to use the longer workaround-form in Swift 3 is frustrating …
Any progress/news on this?

jepers · 2016-07-19T23:05:54Z

Here is a smaller example demonstrating a similar and possibly related issue:

Xcode 7.3.1, Swift 2.2:

extension MutableCollectionType {
    mutating func processEachElementInPlace(op: (inout Generator.Element) -> Void) {
        for index in self.indices { op(&self[index]) }
    }
}
var a = [1, 2, 3, 4]
a.processEachElementInPlace { $0 *= 10 }
print(a) // Prints [10, 20, 30, 40]

Xcode 8 beta 3, Swift 3:

extension MutableCollection where Indices.Iterator.Element == Index {
    mutating func processEachElementInPlace(_ op: (inout Iterator.Element) -> Void) {
        for index in self.indices { op(&self[index]) }
    }
}
var a = [1, 2, 3, 4]
a.processEachElementInPlace { $0 *= 10 } // Error
print(a)

Error: Cannot invoke 'processEachElementInPlace' with an argument list of type '((inout Int) -> ())'

(Also, that where clause has to be there in order for the subscript to compile.)

jepers · 2016-07-25T09:27:05Z

One more shorter way of demonstrating the issue:
This code should compile without modification on both 2.2 and 3:

protocol P {
    associatedtype A
    var v: A { get set }
}
extension P {
    mutating func modifyInPlaceP(using op: (v: inout A) -> Void) {
        op(v: &self.v)
    }
}
struct S<T> : P { var v: T }
extension S {
    mutating func modifyInPlaceS(using op: (v: inout T) -> Void) {
        op(v: &self.v)
    }
}
struct Point { var x, y : Double }

var a = S.init(v: 1)

a.modifyInPlaceS { (v) in v = v * 2 } // OK
a.modifyInPlaceP { (v) in v = v * 2 } // OK

a.modifyInPlaceS { (v) in v *= 3 } // OK
a.modifyInPlaceP { (v) in v *= 3 } // OK in Swift 2.2, ERROR in Swift 3

var b = S.init(v: Point(x: 1, y: 2))

b.modifyInPlaceS { (v) in v.x = 4 } // OK
b.modifyInPlaceP { (v) in v.x = 4 } // OK in Swift 2.2, ERROR in Swift 3

jepers · 2016-08-04T20:03:01Z

Issue remains unsolved in dev snapshot 2016-08-16 (a).
Here's the last example again slightly modified for latest Swift syntax changes:

protocol P {
    associatedtype A
    var v: A { get set }
}
extension P {
    mutating func modifyInPlaceP(using op: (_: inout A) -> Void) {
        op(&self.v)
    }
}
struct S<T> : P { var v: T }
extension S {
    mutating func modifyInPlaceS(using op: (_: inout T) -> Void) {
        op(&self.v)
    }
}
struct Point { var x, y : Double }

var a = S.init(v: 1)

a.modifyInPlaceS { (v) in v = v * 2 } // OK
a.modifyInPlaceP { (v) in v = v * 2 } // OK

a.modifyInPlaceS { (v) in v *= 3 } // OK
a.modifyInPlaceP { (v) in v *= 3 } // OK in Swift 2.2, ERROR in Swift 3

var b = S.init(v: Point(x: 1, y: 2))

b.modifyInPlaceS { (v) in v.x = 4 } // OK
b.modifyInPlaceP { (v) in v.x = 4 } // OK in Swift 2.2, ERROR in Swift 3

swift-ci transferred this issue from apple/swift-issues Apr 25, 2022

AnthonyLatsis added swift 3.0 regression and removed 3.0 regression labels Nov 19, 2022

This issue was closed.

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[SR-1811] Swift 3 regression related to inout closure params and protocols #44420

[SR-1811] Swift 3 regression related to inout closure params and protocols #44420

jepers commented Jun 18, 2016

belkadan commented Jun 20, 2016

jepers commented Jul 19, 2016

jepers commented Jul 19, 2016

jepers commented Jul 25, 2016

jepers commented Aug 4, 2016

[SR-1811] Swift 3 regression related to inout closure params and protocols #44420

[SR-1811] Swift 3 regression related to inout closure params and protocols #44420

Comments

jepers commented Jun 18, 2016

belkadan commented Jun 20, 2016

jepers commented Jul 19, 2016

jepers commented Jul 19, 2016

jepers commented Jul 25, 2016

jepers commented Aug 4, 2016