mrousavy
commented
2 weeks ago Okay I just found out that the offending piece of code is the self.implementation.someCallback = part.
If I just capture the std::function locally, it works ✅:
set {
let captured: (_ num: Double) -> Void = { num in
newValue(num)
}
}But as soon as I capture it and assign it to another property (in my case, implementation is a protocol), it fails ❌:
set {
let captured: (_ num: Double) -> Void = { num in
newValue(num)
}
self.implementation.someCallback = { (num: Double) -> Void in
captured(num)
}
}With this error:
- Global is external, but doesn't have external or weak linkage!
Description
I have a C++
std::function<void(double)>(astd::functionwith arguments) which I want to wrap in a nice Swift closure ((Double) -> Void), to be able to call it later.The C++
std::functionhas some captured state, in my case ashared_ptr, but it is still copyable:My Swift property then wraps this
std::functionas a Swift closure:While this works with an
std::functionwithout arguments (std::function<void()>), it crashes the compiler when using astd::functionwith arguments (std::function<void(double)>)!Reproduction
Stack dump
Expected behavior
I expect the Swift closure to properly capture the
std::function, so I can call it later. After all, it is a copyablestd::function.Environment
swift-driver version: 1.90.11.1 Apple Swift version 5.10 (swiftlang-5.10.0.13 clang-1500.3.9.4) Target: arm64-apple-macosx14.0
Additional information
No response