Get the internal function pointer in swift

peekFunc.swift

/// See
///   https://github.com/rodionovd/SWRoute/wiki/Function-hooking-in-Swift
///   https://github.com/rodionovd/SWRoute/blob/master/SWRoute/rd_get_func_impl.c
/// to find why this works

func peekFunc<A, R>(_ f: @escaping (A) -> R) -> (fp: Int, ctx: Int) {
	typealias IntInt = (Int, Int)
	let (_, lo) = unsafeBitCast(f, to: IntInt.self)
	let offset = MemoryLayout<Int>.size == 8 ? 16 : 12
	let ptr = UnsafePointer<Int>(bitPattern: lo + offset)!
	return (ptr.pointee, ptr.successor().pointee)
}

func === <A, R>(lhs: @escaping (A) -> R, rhs: @escaping (A) -> R) -> Bool {
	let (tl, tr) = (peekFunc(lhs), peekFunc(rhs))
	return tl.0 == tr.0 && tl.1 == tr.1
}


// simple functions
func genericId<T>(t:T)->T { return t }
func incr(i:Int)->Int { return i + 1 }
var f: (Int) -> Int = genericId
var g = f;      print("(f === g) == \(f === g)")
f = genericId;  print("(f === g) == \(f === g)")
f = g;          print("(f === g) == \(f === g)")

// closures
func mkcounter() -> () -> Int {
	var count: Int = 0

	return {
		count += 1
		return count
	}
}

var c0 = mkcounter()
var c1 = mkcounter()
var c2 = c0

print("peekFunc(c0) == \(peekFunc(c0))")
print("peekFunc(c1) == \(peekFunc(c1))")
print("peekFunc(c2) == \(peekFunc(c2))")
print("(c0() == c1()) == \(c0() == c1())") // true : both are called once
print("(c0() == c2()) == \(c0() == c2())") // false: because c0() means c2()
print("(c0 === c1) == \(c0 === c1)")
print("(c0 === c2) == \(c0 === c2)")