Benchmarking ZR

results

$ go test -bench=.
testing: warning: no tests to run
PASS
BenchmarkIntersect1     50000000                29.5 ns/op
BenchmarkIntersect2     50000000                35.5 ns/op

35.5/29.5 = 1,20 

zr.go

package zr

type Point struct {
	X, Y float64
}

type Rectangle struct {
	Min, Max Point
}

var ZR Rectangle

func (r Rectangle) Intersect1(s Rectangle) Rectangle {
	if r.Min.X < s.Min.X {
		r.Min.X = s.Min.X
	}
	if r.Min.Y < s.Min.Y {
		r.Min.Y = s.Min.Y
	}
	if r.Max.X > s.Max.X {
		r.Max.X = s.Max.X
	}
	if r.Max.Y > s.Max.Y {
		r.Max.Y = s.Max.Y
	}
	if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y {
		return ZR
	}
	return r
}

func (r Rectangle) Intersect2(s Rectangle) Rectangle {
	if r.Min.X < s.Min.X {
		r.Min.X = s.Min.X
	}
	if r.Min.Y < s.Min.Y {
		r.Min.Y = s.Min.Y
	}
	if r.Max.X > s.Max.X {
		r.Max.X = s.Max.X
	}
	if r.Max.Y > s.Max.Y {
		r.Max.Y = s.Max.Y
	}
	if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y {
		return Rectangle{}
	}
	return r
}

zr_test.go

package zr

import "testing"

var result1, result2 bool

func BenchmarkIntersect1(b *testing.B) {
	r := Rectangle{Point{0, 0}, Point{1, 1}}
	s := Rectangle{Point{2, 2}, Point{3, 3}}
	for n := 0; n < b.N; n++ {
		i := r.Intersect1(s)
		result1 = i == ZR
	}
}

func BenchmarkIntersect2(b *testing.B) {
	r := Rectangle{Point{0, 0}, Point{1, 1}}
	s := Rectangle{Point{2, 2}, Point{3, 3}}
	for n := 0; n < b.N; n++ {
		i := r.Intersect2(s)
		result2 = i == Rectangle{}
	}
}

C:\prog\tmp\test-go-ZR>%goroot%\bin\go test -bench=. -cpu=1
testing: warning: no tests to run
PASS
BenchmarkIntersect1     100000000               25.2 ns/op
BenchmarkIntersect2     50000000                28.1 ns/op
ok      _/C_/prog/tmp/test-go-ZR        4.211s

C:\prog\tmp\test-go-ZR>%goroot%\bin\go test -bench=. -cpu=1
testing: warning: no tests to run
PASS
BenchmarkIntersect1     100000000               28.4 ns/op
BenchmarkIntersect2     50000000                25.6 ns/op
ok      _/C_/prog/tmp/test-go-ZR        4.407s

I believe they're equivalent w.r.t. performance, see above. So, still curious what was the original reason of introducing ZR & ZP :) As to allocations, I'd expect neither of them is actually GCed, they should both be copied by value (on stack). My suspicion is that the original reason was just to make them easier to write. But I'm still rather surprised they were added.