Cannot store function with lifetime dependence in variable

Development Compiler
1

I have a type that provides a view into its storage using RawSpan. Therefore, the view method has an @lifetime annotation. Because I am interfacing with C, I need to at least save the method in a variable (or get a pointer to the method). However, my friend the compiler keeps telling me Lifetime-dependent value escapes its scope -- which makes sense, I guess. Or is this a bug because the compiler thinks I am invoking the method?

	struct A {
		@lifetime(borrow self)
		func giveMeAChunkOfData(at index: Int, point: Point) -> RawSpan {
			fatalError()
		}
	}
	
	func _parse(_ a: borrowing A) {
		let fn = a.giveMeAChunkOfData(at:point:) // 🛑 Lifetime-dependent value escapes its scope
		withUnsafePointer(to: a.giveMeAChunkOfData(at:point:)) { functionPointer in // 🛑 Lifetime-dependent value escapes its scope
			
		}
	}

A,
Are you prohibited from referencing functions with @lifetime annotations?

B,
how do I temporarily get around the error (using the latest main snapshot)? I know this is unsafe, I would like to acknowledge that fact and still be able to take an address of said method. IRL, it is safe in my case.

Concerning B, I have tried some of the trickery in LifetimeManager.swift in the stdlib (_overrideLifetime functions), even tried 'immortalizing' a and/or giveMeAChunkOfData this way, but no luck there.

cheers

2

Sorry, we don't have the type system support yet for using a closure capture as the source of a lifetime dependency. Not because it's difficult; just lack of time.

On main, you'll get the message:

error: lifetime-dependent value escapes its scope
note: it depends on a closure capture; this is not yet supported

I'm not sure how to work around it short of capturing state in a struct and passing that rather than a function type.