Difference

Better way to identify what's different between 2 instances.

Have you ever written tests? Usually they use equality asserts, e.g. XCTAssertEqual, what happens if the objects aren't equal? Xcode throws a wall of text at you:

This forces you to manually scan the text and try to figure out exactly what's wrong, what if instead you could just learn which property is different?

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Installation

CocoaPods

Add pod 'Difference' to your Podfile.

Carthage

Add github "krzysztofzablocki/Difference" to your Cartfile.

SwiftPM

Add .package(url: "https://github.com/krzysztofzablocki/Difference.git", branch: "master") dependency in your Package manifest.

Using lldb

Write the following to see the difference between 2 instances:

po dumpDiff(expected, received)

Integrate with XCTest

Add this to your test target:

public func XCTAssertEqual<T: Equatable>(_ expected: @autoclosure () throws -> T, _ received: @autoclosure () throws -> T, file: StaticString = #filePath, line: UInt = #line) {
    do {
        let expected = try expected()
        let received = try received()
        XCTAssertTrue(expected == received, "Found difference for \n" + diff(expected, received).joined(separator: ", "), file: file, line: line)
    }
    catch {
        XCTFail("Caught error while testing: \(error)", file: file, line: line)
    }
}

Replace #filePath with #file if you're using Xcode 11 or earlier.

Integrate with Quick

Add this to your test target:

public func equalDiff<T: Equatable>(_ expectedValue: T?) -> Predicate<T> {
    return Predicate.define { actualExpression in
        let receivedValue = try actualExpression.evaluate()

        if receivedValue == nil {
            var message = ExpectationMessage.fail("")
            if let expectedValue = expectedValue {
                message = ExpectationMessage.expectedCustomValueTo("equal <\(expectedValue)>", actual: "nil")
            }
            return PredicateResult(status: .fail, message: message)
        }
        if expectedValue == nil {
            return PredicateResult(status: .fail, message: ExpectationMessage.fail("").appendedBeNilHint())
        }

        return PredicateResult(bool: receivedValue == expectedValue, message: ExpectationMessage.fail("Found difference for " + diff(expectedValue, receivedValue).joined(separator: ", ")))
    }
}

Write the following to see the difference between 2 instances: expect(received).to(equalDiff(expected))

Integrate with The Composable Architecture

If you are using The Composable Architecture nameLabels configuration to get a diff that's more appropiate for reducer instrumentation

diff(oldState, newState, indentationType: .pipe, nameLabels: .comparing)

You can use this function in your own variant of ReducerInstrumentation code based on this

That way your diffs will look more like this:

Received action:
  AppAction.home(.howTo(.setSelectedSlide))
State:
home:
|	selectedHowTo:
|	|	selectedSlide:
|	|	|	Current: 8mnkni91h4fe
|	|	|	Previous: exei4wpqsmdk