Hey gophers, I would like to know your opinion on the following topic.
In my experience, the most popular case for errors.Join
<https://pkg.go.dev/errors#Join> is to handle deferred potential errors
such as closing os.File, sql.Rows or http.Response.Body.
Might be a bit of a contrived example, it get the main point though:
```go
func WriteJSONTo(v any, filename string) (err error) {
file, err := os.OpenFile(filename, os.O_RDWR|os.O_CREATE, 0644)
if err != nil {
return err
}
defer func() { err = errors.Join(err, file.Close()) }()
return json.NewEncoder(file).Encode(v)
}
```
Although such deferred errors are still worth handling, I assume that they
are unlikely to happen. That is, most function calls look like either
`errors.Join(nil, nil)` or `errors.Join(someNonNilErr, nil)`
And the function itself always returns either nil or a wrapped trough
`*errors.joinError` implementation, even if only one non-nil error is
provided.
So, what do you think it makes sense for the function to return a wrapped
error even if it contains only one error? Wouldn't it be more rational in
such cases for Join to return that single error?
In addition, if such a use case occurs quite often, then avoiding
unnecessary allocation could be a pleasant bonus:
```go
func BenchmarkJoinTwoErrors(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = Join(io.EOF, io.ErrNoProgress)
}
}
func BenchmarkJoinOneError(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = Join(io.EOF, nil)
}
}
```
```
goos: linux
goarch: amd64
pkg: fallout
cpu: 12th Gen Intel(R) Core(TM) i9-12900K
│ 1.txt │ 5.txt │
│ sec/op │ sec/op vs base │
JoinTwoErrors-24 20.87n ± 2% 21.18n ± 2% ~ (p=0.075 n=10)
JoinOneError-24 17.010n ± 2% 1.321n ± 1% -92.23% (p=0.000 n=10)
geomean 18.84n 5.290n -71.92%
│ 1.txt │ 5.txt │
│ B/op │ B/op vs base │
JoinTwoErrors-24 32.00 ± 0% 32.00 ± 0% ~ (p=1.000 n=10) ¹
JoinOneError-24 16.00 ± 0% 0.00 ± 0% -100.00% (p=0.000 n=10)
geomean 22.63 ? ² ³
¹ all samples are equal
² summaries must be >0 to compute geomean
³ ratios must be >0 to compute geomean
│ 1.txt │ 5.txt │
│ allocs/op │ allocs/op vs base │
JoinTwoErrors-24 1.000 ± 0% 1.000 ± 0% ~ (p=1.000 n=10) ¹
JoinOneError-24 1.000 ± 0% 0.000 ± 0% -100.00% (p=0.000 n=10)
geomean 1.000 ? ² ³
¹ all samples are equal
² summaries must be >0 to compute geomean
³ ratios must be >0 to compute geomean
```
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