DifferenceKit provides a default implementation of Different

After clone this project and modify the implementation to return <code class="notransl

Unexpected behavior when using the default implementations of `Differentiable` for `Hashable` about differencekit HOT 1 OPEN

ra1028 commented on June 7, 2024 3

Unexpected behavior when using the default implementations of `Differentiable` for `Hashable`

from differencekit.

Comments (1)

yunhao commented on June 7, 2024 1

After clone this project and modify the implementation to return hashValue, the unit test fails at func testSameHashValue(). I'm a little confused about this test case.

DifferenceKit/Tests/AlgorithmTest.swift

Lines 246 to 284 in f8c8d1e

 func testSameHashValue() { 

 struct A: Hashable, Differentiable { 

 let actualValue: Int 

 init(_ actualValue: Int) { 

 self.actualValue = actualValue 

 } 

 func hash(into hasher: inout Hasher) { 

 hasher.combine(0) 

 } 

 func isContentEqual(to source: A) -> Bool { 

 return actualValue == source.actualValue 

 } 

 } 

 let section = 0 

 let source = [A(0), A(1)] 

 let target = [A(0), A(2)] 

 XCTAssertExactDifferences( 

 source: source, 

 target: target, 

 section: section, 

 expected: [ 

 Changeset( 

 data: [A(0)], 

 elementDeleted: [ElementPath(element: 1, section: section)] 

 ), 

 Changeset( 

 data: target, 

 elementInserted: [ElementPath(element: 1, section: section)] 

 ) 

 ] 

 ) 

 } 

 }

I think it should be a update change instead of a delete -> insert change, because they have the same identifier (hasher.combine(0)) and different content.

It seems that DifferenceKit doesn't use the result of func hash(into hasher: inout Hasher). When using Hashable, we can use hasher.combine(identifier) to determine our identifier, but DifferenceKit will ignore it.

from differencekit.

Unexpected behavior when using the default implementations of `Differentiable` for `Hashable` about differencekit HOT 1 OPEN

Comments (1)

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	func testSameHashValue() {
	struct A: Hashable, Differentiable {
	let actualValue: Int

	init(_ actualValue: Int) {
	self.actualValue = actualValue
	}

	func hash(into hasher: inout Hasher) {
	hasher.combine(0)
	}

	func isContentEqual(to source: A) -> Bool {
	return actualValue == source.actualValue
	}
	}

	let section = 0

	let source = [A(0), A(1)]
	let target = [A(0), A(2)]

	XCTAssertExactDifferences(
	source: source,
	target: target,
	section: section,
	expected: [
	Changeset(
	data: [A(0)],
	elementDeleted: [ElementPath(element: 1, section: section)]
	),
	Changeset(
	data: target,
	elementInserted: [ElementPath(element: 1, section: section)]
	)
	]
	)
	}
	}