retains.swift

import Foundation

public func with<T>(_ item: T, update: (inout T) throws -> Void) rethrows -> T {
    var this = item
    try update(&this)
    return this
}

class MyC: NSObject {
}

typealias RetainType = @convention(c) (UnsafeRawPointer, Selector) -> UnsafeRawPointer
let oldRetain = unsafeBitCast(class_getMethodImplementation_stret(MyC.self, sel_getUid("retain")), to: RetainType.self)
let retain: RetainType = { (self: UnsafeRawPointer, _cmd: Selector) -> UnsafeRawPointer in
    print("Retaining")
    return oldRetain(self, _cmd)
}
typealias ReleaseType = @convention(c) (UnsafeRawPointer, Selector) -> Void
let oldRelease = unsafeBitCast(class_getMethodImplementation_stret(MyC.self, sel_getUid("release")), to: ReleaseType.self)
let release: ReleaseType = { (self: UnsafeRawPointer, _cmd: Selector) -> Void in
    print("Releasing")
    oldRelease(self, _cmd)
}
class_addMethod(MyC.self, sel_getUid("retain"), unsafeBitCast(retain, to: IMP.self), "@@:")
class_addMethod(MyC.self, sel_getUid("release"), unsafeBitCast(release, to: IMP.self), "v@:")

while true {
    let task3 = with(MyC()) { _ in
        //    $0.launchPath = "/usr/bin/mdfind"
        //    $0.arguments = ["kMDItemDisplayName == *.playground"]
        //    $0.standardOutput = pipe
//        print($0)
    }
//    print(task3)
}