Open Radar

 
Summary:
Using XCTAssertEqual in Swift with NSObject subclasses can yield different results than using the == operator. This is very confusing.

Steps to Reproduce:
1. Consider the following Objective-C code:

    @import Foundation;
    NSMeasurement *a = [[NSMeasurement alloc] initWithDoubleValue:1 unit:[NSUnitLength kilometers]];
    NSMeasurement *b = [[NSMeasurement alloc] initWithDoubleValue:1000 unit:[NSUnitLength meters]];
    XCTAssertEqual(a, b);

2. And the equivalent Swift code:

        import Foundation
        let a = Measurement(value: 1, unit: UnitLength.kilometers)
        let b = Measurement(value: 1000, unit: UnitLength.meters)
        XCTAssertTrue(a == b)
        XCTAssertEqual(a, b) // fails!!!

Expected Results:
All assertions pass. Specifically, both assertions in the Swift code snippet should have the same result.

Actual Results:
The second assertion in the Swift code snippet, XCTAssertEqual(a, b), fails. This is very unintuitive to me because it has a different result than a == b although XCTAssertEqual has a overload for T: Equatable, so I would assume that it uses a == b internally. For some reason, it XCTAssertEqual seems to fall back on the -isEqual implementation of NSObject that compares object pointers, at least that is the only explanation I have for this behavior.

Regression:
---

Notes:
Is this intended behavior? To me it looks like a bug.