[swift-dev] Exclusivity checker hacking?

[Jordan Rose]

> On Oct 5, 2017, at 13:42, David Zarzycki via swift-dev <swift-dev at swift.org> wrote:
> 
> Hello,
> 
> As an experiment, I’d like to force the exclusivity checking logic to always error at compile time, rather than a mix of compile time and run time. Near as I can tell, there is no built in debugging logic to do this (not even to warn when dynamic checks are added). Am I missing something? Where would be the best place in the code to make the dynamic checker error/warning at compile time? Would a warning be useful to others? Or should I just keep this on a throwaway branch?

It's worth noting that this is impossible in the general case:

// Library.swift
public class Foo {
  public var x: Int = 0
  public init() {}
}
public func testExclusivity(_ a: Foo, _ b: Foo, by callback: (inout Int, inout Int) -> Void) {
  callback(&a.x, &b.x)
}

// Client.swift, compiled as a separate target
let foo = Foo()
testExclusivity(foo, foo) { $0 = 42; $1 = 8192 }

That doesn't necessarily mean there aren't improvements to be made, but it might change your goals.

Jordan

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