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[SR-4949] No error for using 'as' patterns with CF types #47526

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belkadan opened this issue May 19, 2017 · 5 comments
Open

[SR-4949] No error for using 'as' patterns with CF types #47526

belkadan opened this issue May 19, 2017 · 5 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation good first issue Good for newcomers

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@belkadan
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Previous ID SR-4949
Radar rdar://problem/32255478
Original Reporter @belkadan
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, StarterBug
Assignee None
Priority Medium

md5: 62d9e9e2da2d4b28fa3d10ebd350dba6

Issue Description:

import Foundation

let x = ([1: 2] as NSDictionary) as Any

switch x {
case let b as CFBoolean:
    print("it's a cfbool: \(b)")
    
default:
    print("n/a")
}

We should warn here that we can't actually do checked downcasts for CF types, like we do with as?.

import Foundation
let x = ([1: 2] as NSDictionary) as Any
let y = x as? CFDictionary // error: conditional downcast to CoreFoundation type 'CFDictionary' will always succeed

We can't make it an error because that would break source compatibility, but at least a warning will work. The best workaround today (and a possible fix-it):

switch x {
case let rawB:
    let b = rawB as! CFBoolean
    print("it's a cfbool: \(b)")
    
default:
    print("n/a")
}
@swift-ci
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swift-ci commented Jun 9, 2017

Comment by Dmitry Venikov (JIRA)

What warning message should be used?

@belkadan
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I think it's okay to reuse the message that as? uses (but as a warning).

@swift-ci
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Comment by Dmitry Venikov (JIRA)

Finally I'm starting to investigate this issue.

{code:swift}case let b as CFBoolean

@belkadan
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Resetting assignee for all Starter Bugs not modified since 2018.

@theblixguy
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I think the runtime should support this by calling CFGetTypeID and then performing a cast... or maybe we can insert an implicit check instead.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation good first issue Good for newcomers
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@belkadan @theblixguy @swift-ci