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

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).

@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.

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.

@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.

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.

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

@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.

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

Yes. I guess I'm confused. What are you asking for?

io.MultiCloser and io.MultiWriteCloser

Thanks, but I don't think we're going to do that, per @bradfitz's comment above. they can be written in a third party library just as effectively.

I don't agree with @bradfitz's argument. Is the purpose of the standard library to serve itself? Of course not. If the use case for users of the standard library is compelling, then the standard library should be updated even if the features don't see internal use within the standard library.

But this is the kind of functionality that can easily be written outside of the standard library. For this kind of thing, that is the place to start. Then if it proves to be popular, it can be brought in.

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

I am familiar with that policy, and in most cases I would agree. But this is a case where the new feature is simple and addresses a defect in the stdlib - that we have a MultiWriter but not the equivalents for Closer and WriteCloser doesn't make sense. It's like only a third of the work was done, not like an entirely new feature is being proposed.