Can't pass empty int slices

[gbl08ma]

I have a IntSliceVar flag called groups. I can't seem to be able to pass empty slices in any way:

If I use --groups=[],
Error: invalid argument "[]" for "--groups" flag: strconv.Atoi: parsing "[]": invalid syntax

If I use --groups="",
Error: invalid argument "" for "--groups" flag: strconv.Atoi: parsing "": invalid syntax

Is there another syntax I'm missing?
This is part of a command-line program that uses cobra but I believe the problem to be within pflag (even though the error handling, that is printing the above errors and returning before I can get to my command handler, appears to be within cobra).

[hoshsadiq]

What is the use-case here? Why do you need to pass in an empty integer? That would just be 0 wouldn't it?

[gbl08ma]

It's not an empty integer, it's an empty integer slice.

[hoshsadiq]

Oh right. I misread. I'm still curious what the use-case is. Why do you need to pass in an empty slice? Can you not set empty slice as a default and avoid passing in the flag at all?

[gbl08ma]

The use case is implementing the following interface on a command to edit a resource:

• Absence of flag: the field is not edited at all
• Presence of flag with empty slice: the field is edited to become the empty list
• Presence of flag with non-empty slice: the field is edited to become the passed list

[zerkms]

Happy to deliver a PR with implementation if dev team agrees this feature is welcome :-)

Proposed behaviour: --groups= (assuming it's defined as a IntSliceVar) should result to []int{}.

[tomasaschan]

This issue has not been updated in a long time. Is it still relevant?

(If I receive no answer before the end of the summer, I'll close it. Feel free to re-open if you come here after that happens and it is relevant to you - but if you do, please also comment and specify what outcome you're interested in!)

[zerkms]

It is still relevant - there is still no way to pass an empty slice value.

Eg:

for

cmd.Flags().IntSliceVar(&data, "data", []int{}, "data values to look for")

and --data= passed as command line arguments it returns

Error: invalid argument "" for "--data" flag: strconv.Atoi: parsing "": invalid syntax

error. --data=[] returns Error: invalid argument "[]" for "--data" flag: strconv.Atoi: parsing "[]": invalid syntax.

Version used for repro:

github.com/spf13/pflag v1.0.7 h1:vN6T9TfwStFPFM5XzjsvmzZkLuaLX+HS+0SeFLRgU6M=
github.com/spf13/pflag v1.0.7/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=

[tomasaschan]

I think allowing --data= to represent an empty slice sounds reasonable, since --data= currently results in an error (so the syntax is available, so to speak) and the current syntax for providing a non-empty slice is a list of comma-separated values (so the empty string is a clean extension of the existing functionality). Feel free to send a PR!

I think a few tests that should be present in that PR are

• passing --data= results in the expected (non-nil) empty slice
• not passing the flag results in a preserved default value, regardless of whether that default value is nil, an empty slice, or a non-empty slice

[zerkms]

Feel free to send a PR!

That's what I suggested 2 years ago too :-D #222 (comment)

I'm still keen to do that, but please nobody please take my word on it and if someone needs it quicker and/or has some free time before me - please go ahead and don't wait.