ios - CIImage 应该是平等的吗？

Question

因此，Apple 的文档说 CIImage 符合 Equatable。我认为这意味着以下单元测试将通过。然而，事实并非如此。我很想知道为什么。

func test_CIImageEqualityShouldWork() {
    let bundle = NSBundle(forClass: PrototypeTests.self)
    guard let path = bundle.pathForResource("testImage", ofType: "png") else { return }
    guard let image = UIImage(contentsOfFile: path) else { return }

    let thingy1 = CIImage(image: image)
    let thingy2 = CIImage(image: image)
    XCTAssert(thingy1 == thingy2)
}

图像存在，guard 语句都通过了，但是 assert 失败了，它们不相等。

出于兴趣，我尝试创建了两次 UIImage 并进行了比较。那也失败了。

Answer 1

所有NSObject子类都符合Equatable，==函数在对象上调用 isEqual: 方法。 isEqual: 方法NSObject 只是比较对象指针，即 o1 == o2如果 o1 和 o2 引用相同的对象实例则成立。

例子见 Interacting with Objective-C APIs :

Swift provides default implementations of the == and === operators and adopts the Equatable protocol for objects that derive from the NSObject class. The default implementation of the == operator invokes the isEqual: method, and the default implementation of the === operator checks pointer equality. You should not override the equality or identity operators for types imported from Objective-C.

The base implementation of the isEqual: provided by the NSObject class is equivalent to an identity check by pointer equality.

许多 NSObject 子类覆盖了 isEqual: 方法(例如 NSString，NSArray, NSDate, ...) 但不是 CIImage:

let thingy1 = CIImage(image: image)
let thingy2 = CIImage(image: image)

创建两个不同的 CIImage 实例并将它们比较为“不相等”。