"Experiment to measure the difference in running time between our potentially inefficient versions and the one that uses strings.Join. (Section 1.6 illustrates part of the time package, and Section 11.4 shows how to write benchmark tests for systematic performance evaluation.)"
See echo1 and echo3 for the different versions.
$ go test -bench=. -benchmem
goos: windows
goarch: amd64
pkg: github.com/masonelmore/gopl/ch1/ex1.3
benchmark iter time/iter bytes alloc allocs
--------- ---- --------- ----------- ------
BenchmarkEchoConcat/0-12 500000000 3.22 ns/op 0 B/op 0 allocs/op
BenchmarkEchoConcat/10-12 2000000 798.00 ns/op 416 B/op 9 allocs/op
BenchmarkEchoConcat/100-12 50000 30661.00 ns/op 30960 B/op 99 allocs/op
BenchmarkEchoConcat/1000-12 500 2756157.00 ns/op 3238064 B/op 999 allocs/op
BenchmarkEchoConcat/10000-12 5 202611580.00 ns/op 325934566 B/op 9999 allocs/op
BenchmarkEchoConcat/100000-12 1 13021744800.00 ns/op 30350007968 B/op 100082 allocs/op
BenchmarkEchoJoin/0-12 300000000 5.87 ns/op 0 B/op 0 allocs/op
BenchmarkEchoJoin/10-12 5000000 260.00 ns/op 160 B/op 2 allocs/op
BenchmarkEchoJoin/100-12 1000000 1888.00 ns/op 1280 B/op 2 allocs/op
BenchmarkEchoJoin/1000-12 100000 12110.00 ns/op 12288 B/op 2 allocs/op
BenchmarkEchoJoin/10000-12 10000 183210.00 ns/op 131072 B/op 2 allocs/op
BenchmarkEchoJoin/100000-12 1000 1871107.00 ns/op 1212416 B/op 2 allocs/op
ok github.com/masonelmore/gopl/ch1/ex1.3 33.360s