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reflect: export DeepValueEqual #32321

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masterada opened this issue May 30, 2019 · 2 comments
Closed

reflect: export DeepValueEqual #32321

masterada opened this issue May 30, 2019 · 2 comments
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FeatureRequest Issues asking for a new feature that does not need a proposal. FrozenDueToAge Performance WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided.

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@masterada
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I have two values with type reflect.Value. I would like to call reflect.DeepEquals on them. Currently I'm doing it this way:

reflect.DeepEqual(v1.Interface(), v2.Interface())

This seems like a waste of cpu time, as DeepEqual will just wrap them again with reflect.Value.

Would it be possible to add a method like this?

func DeepValueEqual(v1, v2 Value) bool {
	if v1.Type() != v2.Type() {
		return false
	}
	return deepValueEqual(v1, v2, make(map[visit]bool), 0)
}
@mvdan
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mvdan commented May 30, 2019

If this proposal is based on performance, have you measured the impact with a benchmark? You could use simple values, so that the comparison itself is little work.

@bcmills bcmills added FeatureRequest Issues asking for a new feature that does not need a proposal. Performance WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. labels May 30, 2019
@masterada
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very suprising results, never imagined converting string to interface would take up half the time:

code:


var e bool

func benchmarkDeepEqual(b *testing.B, s1 string, s2 string) {
	var i1 interface{} = s1
	var i2 interface{} = s2

	v1 := reflect.ValueOf(s1)
	v2 := reflect.ValueOf(s2)

	b.Run("DeepEqual_string", func(b *testing.B) {
		for n := 0; n < b.N; n++ {
			e = reflect.DeepEqual(s1, s2)
		}
	})

	b.Run("DeepEqual_interface", func(b *testing.B) {
		for n := 0; n < b.N; n++ {
			e = reflect.DeepEqual(i1, i2)
		}
	})

	b.Run("DeepEqual_Value", func(b *testing.B) {
		for n := 0; n < b.N; n++ {
			e = reflect.DeepEqual(v1.Interface(), v2.Interface())
		}
	})

	b.Run("DeepValueEqual", func(b *testing.B) {
		for n := 0; n < b.N; n++ {
			e = reflect.DeepValueEqual(v1, v2)
		}
	})
}

func BenchmarkDeepEqual_eq(b *testing.B)  { benchmarkDeepEqual(b, "test", "test") }
func BenchmarkDeepEqual_neq(b *testing.B) { benchmarkDeepEqual(b, "test", "test2") }

results:

BenchmarkDeepEqual_eq/DeepEqual_string-4         	10000000	       144 ns/op
BenchmarkDeepEqual_eq/DeepEqual_interface-4      	20000000	        78.1 ns/op
BenchmarkDeepEqual_eq/DeepEqual_Value-4          	20000000	        91.3 ns/op
BenchmarkDeepEqual_eq/DeepValueEqual-4           	20000000	        73.0 ns/op
BenchmarkDeepEqual_neq/DeepEqual_string-4        	10000000	       142 ns/op
BenchmarkDeepEqual_neq/DeepEqual_interface-4     	20000000	        72.1 ns/op
BenchmarkDeepEqual_neq/DeepEqual_Value-4         	20000000	        88.4 ns/op
BenchmarkDeepEqual_neq/DeepValueEqual-4          	20000000	        67.7 ns/op

@golang golang locked and limited conversation to collaborators May 29, 2020
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FeatureRequest Issues asking for a new feature that does not need a proposal. FrozenDueToAge Performance WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided.
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@mvdan @masterada @bcmills @gopherbot