Benchmarks to compare the different string concatenation methods in Go
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README.md

go-string-concat-benchmarks

Benchmarks to compare the different string concatenation methods in Go. For all the details, see stringconcat_test.go.

There is also a blog post detailing the methodology and results.

In summary, for very few concatenations of short strings (fewer than hundred, length shorter than 10) using naive string appending is just fine. For more heavy-duty cases where efficiency is important, bytes.Buffer is the best choice out of the methods evaluated. strings.Join is a good choice when you already have a string slice that just needs to be concatenated into one string.

Here are how the methods tested stack up:

Comparison of string concatenation methods in Go

And here are the raw results (also including a benchmark for byte slices):

BenchmarkNaiveConcat10-3     	 2000000	      1192 ns/op	     360 B/op	      11 allocs/op
BenchmarkNaiveConcat100-3    	   50000	     34117 ns/op	   26408 B/op	     101 allocs/op
BenchmarkNaiveConcat1000-3   	     500	   2641900 ns/op	 2694414 B/op	    1004 allocs/op
BenchmarkNaiveConcat10000-3  	      10	 188733914 ns/op	271630262 B/op	   10339 allocs/op
BenchmarkByteSlice10-3       	 2000000	       717 ns/op	     208 B/op	       7 allocs/op
BenchmarkByteSlice100-3      	  300000	      4000 ns/op	    1552 B/op	      10 allocs/op
BenchmarkByteSlice1000-3     	   30000	     53874 ns/op	   26128 B/op	      16 allocs/op
BenchmarkByteSlice10000-3    	    2000	    701131 ns/op	  283668 B/op	      24 allocs/op
BenchmarkByteSliceSize10-3   	 3000000	       536 ns/op	     200 B/op	       4 allocs/op
BenchmarkByteSliceSize100-3  	  300000	      3396 ns/op	    1560 B/op	       4 allocs/op
BenchmarkByteSliceSize1000-3 	   30000	     40858 ns/op	   15896 B/op	       4 allocs/op
BenchmarkByteSliceSize10000-3	    2000	    575724 ns/op	  163866 B/op	       4 allocs/op
BenchmarkJoin10-3            	 1000000	      1724 ns/op	     648 B/op	       9 allocs/op
BenchmarkJoin100-3           	  200000	      9183 ns/op	    5128 B/op	      12 allocs/op
BenchmarkJoin1000-3          	   20000	     82654 ns/op	   43528 B/op	      15 allocs/op
BenchmarkJoin10000-3         	    1000	   1540246 ns/op	  941844 B/op	      24 allocs/op
BenchmarkJoinSize10-3        	 2000000	       887 ns/op	     312 B/op	       5 allocs/op
BenchmarkJoinSize100-3       	  200000	      5981 ns/op	    2712 B/op	       5 allocs/op
BenchmarkJoinSize1000-3      	   20000	     66210 ns/op	   27160 B/op	       5 allocs/op
BenchmarkJoinSize10000-3     	    2000	    814003 ns/op	  278555 B/op	       5 allocs/op
BenchmarkBufferString10-3    	 1000000	      1354 ns/op	     400 B/op	       8 allocs/op
BenchmarkBufferString100-3   	  200000	      6410 ns/op	    2368 B/op	      11 allocs/op
BenchmarkBufferString1000-3  	   20000	     56510 ns/op	   18880 B/op	      14 allocs/op
BenchmarkBufferString10000-3 	    2000	    699816 ns/op	  170178 B/op	      17 allocs/op
BenchmarkBufferSize10-3      	 2000000	       766 ns/op	     312 B/op	       5 allocs/op
BenchmarkBufferSize100-3     	  300000	      4548 ns/op	    1672 B/op	       5 allocs/op
BenchmarkBufferSize1000-3    	   30000	     50437 ns/op	   16008 B/op	       5 allocs/op
BenchmarkBufferSize10000-3   	    2000	    670182 ns/op	  163978 B/op	       5 allocs/op