What is the best way to test for an empty string in Go

Question

Which method is best  more idomatic  for testing non-empty strings  in Go    if len mystring   gt  0       Or   if mystring             Or something else

User · Answer

Assuming that empty spaces and all leading and trailing white spaces should be removed:

import "strings"
if len(strings.TrimSpace(s)) == 0 { ... }

Because :
len("") // is 0
len(" ") // one empty space is 1
len(" ") // two empty spaces is 2

User · Answer

This seems to be premature microoptimization  The compiler is free to produce the same code for both cases or at least for these two  if len s     0           and  if s                 because the semantics is clearly equal

User · Answer

It would be cleaner and less error-prone to use a function like the one below   func empty s string  bool       return len strings TrimSpace s      0

User · Answer

As of now  the Go compiler generates identical code in both cases  so it is a matter of taste  GCCGo does generate different code  but barely anyone uses it so I wouldn t worry about that   https   godbolt org z fib1x1

User · Answer

Checking for length is a good answer  but you could also account for an  empty  string that is also only whitespace  Not  technically  empty  but if you care to check   package main  import      fmt     strings     func main       stringOne     merpflakes    stringTwo            stringThree          if len strings TrimSpace stringOne      0       fmt Println  String is empty           if len strings TrimSpace stringTwo      0       fmt Println  String two is empty           if len stringTwo     0       fmt Println  String two is still empty           if len strings TrimSpace stringThree      0       fmt Println  String three is empty

User · Answer

This would be more performant than trimming the whole string  since you only need to check for at least a single non-space character existing      Strempty checks whether string contains only whitespace or not func Strempty s string  bool       if len s     0           return true            r      rune s      l    len r       for l  gt  0           l--         if  unicode IsSpace r l                 return false                      return true

User · Answer

As per official guidelines and from performance point of view they appear equivalent  ANisus answer   the s       would be better due to a syntactical advantage  s       will fail at compile time if the variable is not a string  while len s     0 will pass for several other data types

User · Answer

Just to add more to comment  Mainly about how to do performance testing   I did testing with following code   import        testing     var ss     string  Hello        bar         baz    ewrqlosakdjhf12934c r39yfashk fjkashkfashds fsdakjh-        123    func BenchmarkStringCheckEq b  testing B        c    0     b ResetTimer       for n    0  n  lt  b N  n                 for    s    range ss                       if s                                     c                                                  t    2   b N     if c    t               b Fatalf  did not catch empty strings   d     d   c  t          func BenchmarkStringCheckLen b  testing B        c    0     b ResetTimer       for n    0  n  lt  b N  n                 for    s    range ss                        if len s     0                               c                                                  t    2   b N     if c    t               b Fatalf  did not catch empty strings   d     d   c  t          func BenchmarkStringCheckLenGt b  testing B        c    0     b ResetTimer       for n    0  n  lt  b N  n                 for    s    range ss                       if len s   gt  0                               c                                                  t    6   b N     if c    t               b Fatalf  did not catch empty strings   d     d   c  t          func BenchmarkStringCheckNe b  testing B        c    0     b ResetTimer       for n    0  n  lt  b N  n                 for    s    range ss                       if s                                     c                                                  t    6   b N     if c    t               b Fatalf  did not catch empty strings   d     d   c  t            And results were     for a in   seq 50  do go test -run    -bench   --benchtime 1s       grep Bench done   tee -a log   sort -k 3n log   head -10  BenchmarkStringCheckEq-4        150149937            8 06 ns op BenchmarkStringCheckLenGt-4     147926752            8 06 ns op BenchmarkStringCheckLenGt-4     148045771            8 06 ns op BenchmarkStringCheckNe-4        145506912            8 06 ns op BenchmarkStringCheckLen-4       145942450            8 07 ns op BenchmarkStringCheckEq-4        146990384            8 08 ns op BenchmarkStringCheckLenGt-4     149351529            8 08 ns op BenchmarkStringCheckNe-4        148212032            8 08 ns op BenchmarkStringCheckEq-4        145122193            8 09 ns op BenchmarkStringCheckEq-4        146277885            8 09 ns op   Effectively variants usually do not reach fastest time and there is only minimal difference  about 0 01ns op  between variant top speed   And if I look full log  difference between tries is greater than difference between benchmark functions   Also there does not seem to be any measurable difference between BenchmarkStringCheckEq and BenchmarkStringCheckNe or BenchmarkStringCheckLen and BenchmarkStringCheckLenGt even if latter variants should inc c 6 times instead of 2 times   You can try to get some confidence about equal performance by adding tests with modified test or inner loop  This is faster   func BenchmarkStringCheckNone4 b  testing B        c    0     b ResetTimer       for n    0  n  lt  b N  n                 for        range ss                       c                           t    len ss    b N     if c    t               b Fatalf  did not catch empty strings   d     d   c  t            This is not faster   func BenchmarkStringCheckEq3 b  testing B        ss2    make   string  len ss       prefix     a      for i       range ss               ss2 i    prefix   ss i            c    0     b ResetTimer       for n    0  n  lt  b N  n                 for    s    range ss2                       if s    prefix                               c                                                 t    2   b N     if c    t               b Fatalf  did not catch empty strings   d     d   c  t            Both variants are usually faster or slower than difference between main tests   It would also good to generate test strings  ss  using string generator with relevant distribution  And have variable lengths too   So I don t have any confidence of performance difference between main methods to test empty string in go   And I can state with some confidence  it is faster not to test empty string at all than test empty string  And also it is faster to test empty string than to test 1 char string  prefix variant

User · Answer

I think the best way is to compare with blank string  BenchmarkStringCheck1 is checking with blank string  BenchmarkStringCheck2 is checking with len zero  I check with the empty and non-empty string checking  You can see that checking with a blank string is faster   BenchmarkStringCheck1-4     2000000000           0 29 ns op        0 B op          0 allocs op BenchmarkStringCheck1-4     2000000000           0 30 ns op        0 B op          0 allocs op   BenchmarkStringCheck2-4     2000000000           0 30 ns op        0 B op          0 allocs op BenchmarkStringCheck2-4     2000000000           0 31 ns op        0 B op          0 allocs op   Code  func BenchmarkStringCheck1 b  testing B        s     Hello      b ResetTimer       for n    0  n  lt  b N  n             if s                             func BenchmarkStringCheck2 b  testing B        s     Hello      b ResetTimer       for n    0  n  lt  b N  n             if len s     0

User · Answer

Both styles are used within the Go s standard libraries   if len s   gt  0           can be found in the strconv package  http   golang org src pkg strconv atoi go  if s                 can be found in the encoding json package  http   golang org src pkg encoding json encode go  Both are idiomatic and are clear enough  It is more a matter of personal taste and about clarity   Russ Cox writes in a golang-nuts thread      The one that makes the code clear    If I m about to look at element x I typically write   len s    x  even for x    0  but if I care about    is it this specific string  I tend to write s               It s reasonable to assume that a mature compiler will compile   len s     0 and s       into the same  efficient code             Make the code clear    As pointed out in Timmmm s answer  the Go compiler does generate identical code in both cases

[string] What is the best way to test for an empty string in Go?

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