Swift中的通用函数参数指向无效的内存

Question

I'll start with an example setup.

class Parent {
    let parentProperty = 1
}
class Child : Parent {
    let childProperty = 2
}
class Test {
    func testMethod<T : Parent>(data: T) {
        // (llbd) print data
    }
}

let child = Child()
let test = Test()
// (lldb) print child
test.testMethod(child)

I paused execution on places marked with comment "(lldb) print ..." and executed "print child/data" command in debugger console in Xcode.

Output from said commands are listed below.

// print child

(RingRingTests.Child) $R0 = 0x00007fcb886459a0 {
  RingRingTests.Parent = {
    parentProperty = 1
  }
  childProperty = 2
}

// print data

(RingRingTests.Child) $R1 = 0x0000000115a93818 {
  RingRingTests.Parent = {
    parentProperty = 140512143366480
  }
  childProperty = 4294967299
}

The child and data variables obviously point to different location in memory. (being that data point to some invalid memory)

This seems to be like the most basic setup for generic function is swift, nevertheless it is failing.

I guess I'm doing something fundamentally wrong. Can somebody point me to the right direction? Thank you.

Answer 1

I've tried to replace your proposed lldb-tests with plain old debug output and all works fine.

class Parent: CustomDebugStringConvertible {
    let parentProperty = 1
    var debugDescription: String { return "\(parentProperty)" }
}
class Child: Parent {
    let childProperty = 2
    override var debugDescription: String { return "\(parentProperty), \(childProperty)" }
}
class Test {
    func testMethod<T : Parent>(data: T) {
        print(data)
    }
}

let child = Child()
let test = Test()
print(child) // 1, 2
test.testMethod(child) // 1, 2

Some optimisation can screw lldb-tests, but optimisation should not be done for debug builds.

In other words, my answer is "it's actually all right with your code, but maybe something is wrong with your tests".