proposal: io: there should be a multicloser

[GrimTheReaper]

I propose there be a multi-closer like struct inside of io/multi.go. The purpose would be that multiple close objects could be returned under one. Since there are already multi objects, (ie: reader/writer), it makes sense to me to also include multistructs for other things as well, including io.closer.

https://go-review.googlesource.com/c/41814/

[bradfitz]

Where would this be used?

Generally we don't add things to the standard library unless they're common.

See also: https://golang.org/doc/faq#x_in_std

[IngCr3at1on]

I would imagine this would get somewhere around the same amount of usage as a MultiWriter or MultiReader (which I can't say I've ever had a reason to use myself lol).

[GrimTheReaper]

@bradfitz
One use would be used where a function must return a closer, while having multiple things to close, in order to fulfill the interface of io.Closer.

But the point of this proposal is to complete the functionality of src/io/multi.go. In my mind it feels like it is missing.

[bradfitz]

One use would be used where a function must return a closer, while having multiple things to close, in order to fulfill the interface of io.Closer.

Yes, but where concretely? Could you find places in the standard library where code would be simplified by using this.

In previous proposals where things are added to the standard library, the commit or the immediately following one updates the standard library to use the new feature. For instance, when I added strings.Contains in e198a50, the following commit b0afb93 used it. When time.Until was added in 67ea710, the following commit 298791a used it. When sort.Slice was added in 22a2bdf, the following commit ad26bb5 used it.

Where would you use this?

But the point of this proposal is to complete the functionality of src/io/multi.go.

That by itself doesn't meet the bar for standard library inclusion, especially this late in the game. It needs to be simplify existing code.

[GrimTheReaper]

@bradfitz
When you put it like that, it makes sense not to include this into the standard library. I'll be closing this Issue for now.

[ddevault]

Apologies for bumping this, but it's something I was looking for today. I would like to be able to close a MultiWriter and close all of the underlying io.CloseWriters.

[ddevault]

Just ended up in this thread again after hitting a need for this in an unrelated project.

[ianlancetaylor]

@SirCmpwn I don't think what you are asking for (closing an io.MultiWriter is the same as what this CL is about (closing a set of io.Closer values). An io.MultiWriter is a collection of io.Writer values, not io.WriteCloser values.

[ddevault]

An io.MultiWriter only implements io.Writer, not io.Closer. It cannot be closed.