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[SR-11738] PropertyWrapper with Optional type can be used with non-optional type, results in Optional type #54145

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krzyzanowskim opened this issue Nov 8, 2019 · 2 comments
Closed

[SR-11738] PropertyWrapper with Optional type can be used with non-optional type, results in Optional type #54145

krzyzanowskim opened this issue Nov 8, 2019 · 2 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself property wrappers Feature: property wrappers

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@krzyzanowskim
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Previous ID SR-11738
Radar None
Original Reporter @krzyzanowskim
Type Bug
Status Closed
Resolution Done
Environment

Apple Swift version 5.1.2 (swiftlang-1100.0.278 clang-1100.0.33.9)

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

md5: 44cdbf3385c675c2ca0b4f71f6fbd192

duplicates:

  • SR-11443 Property Wrapper overwrites type declaration

Issue Description:

PropertyWrapper with Optional type can be used with non-optional type, results in Optional type

    @propertyWrapper
    struct Wrap<T> {
      var wrappedValue: T?
    }
    
    class Foo {
      @Wrap()
      var name: String // Non-optional declaration
    }
    
    // What is the type of `Foo.name`
    let foo = Foo()
    type(of:foo.name) // String?

It looks like a bug to me. Compiler should throw an error about type mismatch for String and Optional<String>, shouldn't it?
@rnapier
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rnapier commented Nov 8, 2019

I believe this is a dupe of SR-11443.

@theblixguy
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This is fixed on Xcode 11.2.1.

Property type 'String' does not match that of the 'wrappedValue' property of its wrapper type 'Wrap'

However, there's another (separate) bug here - the wrapper is being default-initialised (by doing @Wrap()), which is somehow interfering with the diagnosis of the type mismatch, but that seems to be resolved on 5.2.

error: generic parameter 'T' could not be inferred
          @Wrap() var name: String // Non-optional declaration
           ^
note: 'T' declared as parameter to type 'Wrap'
        struct Wrap<T> {
                    ^
error: cannot convert value of type 'String' to specified type 'T?'
          @Wrap() var name: String // Non-optional declaration
           ^~~~~~

In the meantime, don't default initialize the wrapper (i.e. change @Wrap() to @Wrap).

@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 property wrappers Feature: property wrappers
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@rnapier @krzyzanowskim @theblixguy