Go by Example: Performance: Slice-Append

Compare and benchmark 3 kinds of slice append ref: Arrays, slices (and strings): The mechanics of ‘append’ ref: Golang slice append vs assign performance
	package main
	const length = 1000
1) `genByAppend` will encountered several times of re-allocation as the slice grows. Process includes: - re-allocate a new array with doubled size - copy the existing array data to new one - change the slice pointer to array - append	func genByAppend() []int { var s []int for i := 0; i < length; i++ { s = append(s, i) } return s }
2) `genByAppendCap` pre-allocated the capacity of `length` - already allocated enough space. - should not trigger the re-allocation - however the local variable s (which is a slice header) has to be updated in each cycle of the loop.	func genByAppendCap() []int { s := make([]int, 0, length) for i := 0; i < length; i++ { s = append(s, i) }
	return s }
3) `genByAssign` is the fastest among 3, because of directly assignment.	func genByAssign() []int { s := make([]int, length) for i := 0; i < length; i++ { s[i] = i } return s }

$ go test -v -bench=.

goos: darwin
goarch: arm64
pkg: github.com/hhow09/gobyexample/examples/performance-slice-append
BenchmarkGenByAppend
BenchmarkGenByAppend-8            563953              2148 ns/op
BenchmarkGenByAppendCap
BenchmarkGenByAppendCap-8        2595301               455.5 ns/op
BenchmarkGenByAssign
BenchmarkGenByAssign-8           4048084               294.9 ns/op
PASS
ok      github.com/hhow09/gobyexample/examples/performance-slice-append 5.483s

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