alias, alias, alias. Alias multiple module with same parent more easily

[Paul Smith]

Sometimes aliases get out of hand and either need to be extracted (not always ideal) or take up lots of space and are somewhat tedious to write and read through.

The example below is a common scenario when writing a Phoenix app. Would some kind of syntax like this be helpful?

defmodule
  # Same as writing
  # alias MyApp.Post
  # alias MyApp.User
  # alias MyApp.Comment
  # alias MyApp.Repo
  alias MyApp, [Post, User, Comment, Repo]
end

[José Valim]

I remember this discussion appeared in the past and one of the proposals was to use {...} as delimiter:

    alias MyApp.{Post, User, Comment, Repo}

I can't remember though which language was mentioned (Python or Java?) that provides similar functionality.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Lead Developer

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[Joe Honzawa]

Awesome proposing. I have wanted this feature since before.

+1 to José's idea.

Such notation is familiar to us, in shell.

$ mkdir dir{1,2,3}

> which language was mentioned (Python or Java?) that provides similar functionality.

It is similar to scala's import

import java.util.{ List => JavaList, Map => JavaMap }

2015年3月21日土曜日 0時49分16秒 UTC+9 José Valim:

[Andrea Leopardi]

I'm extremely +1 on this, since it's a feature I often desired myself.

As for the syntax, I think the one proposed by Paul (alias MyApp, [Post, User, Comment, Repo]) is the cleanest one, the easiest to remember and probably the more "programmable" too (the array can be built up programmatically). 

[José Valim]

I'm extremely +1 on this, since it's a feature I often desired myself.

As for the syntax, I think the one proposed by Paul (alias MyApp, [Post, User, Comment, Repo]) is the cleanest one, the easiest to remember and probably the more "programmable" too (the array can be built up programmatically). 

Because alias is lexical, it requires all the arguments to be given explicitly at compile time. So you can't do this:

foo = [Post, User]

bar = [Comment, Repo]

alias MyApp, foo ++ bar

If you want to do it somewhat dynamically, you'd need a macro, and then we are talking about doing:

alias MyApp, unquote(aliases)

Or:

alias MyApp.{unquote_splicing(aliases)}

Which are pretty much the same in terms of complexity. If you are using macros, you need to learn about splicing anyway, if you ever want to generate tuples, lists and function arguments dynamically.

So I would say both are equally programmable. :)

[Andrea Leopardi]

Ah, didn't think about it. Nice!

I still think using a list may be more readable, but these are low-level details, what I want is this feature no matter how :).

Andrea Leopardi

an.le...@gmail.com

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[José Valim]

Yes, it is still arguable which one is better, I was just discussing that particular point view. :)

One thing I don't like about the list is that they are a big ambiguous with the existing options:

alias Foo, [as: Bar]

alias Foo, [Bar, Baz, Bat]

We also need to consider if we are adding the same to require and import too (require mainly). Today, we can actually do:

require Foo.Bar, as: true

And that is equivalent to:

require Foo.Bar, as: Bar

The "as: true" option is not super clear though. We may consider changing that but imagine someone should be able to do something like:

require Foo.{Bar, Baz}, as: true # alias and requires in one step

or:

require Foo, [Bar, Baz], as: true

We need to consider all those scenarios.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Lead Developer

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[Paul Smith]

Thoughts on this? I think this would resolve your concerns, but I'm not sure. 

alias [Post, User, Comment, Repo], from: MyApp

If we don't like this syntax, I think `alias MyApp{Post, User, Comment, Repo} makes the most sense.

I might be able to work on adding this once we decide what we want, but I might need some guidance on how to do so.

[José Valim]

Thanks Paul! I will need to write a proposal and consider how require and import will be affected too. It won't happen soon though, I will ping back here once I do. hopefully you will be able to use the proposal as a guide for your implementation 

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[Θήρων Börner]

José, have you made any progress on a proposal?

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[José Valim]

A proposal considering the different directives, macros, as well as parser changes and the required validation has been written: https://github.com/elixir-lang/elixir/issues/3646

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Aleksei Magusev]

The support for it has just recently been merger into master: https://github.com/elixir-lang/elixir/pull/3666.

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[moloney...@gmail.com]

1 level deep multi alias: (works)

alias MyApp.{Repo, UserManager.User, UserManager.Mail}

2 level deep multi alias (nested multi alias): (not supported)

alias MyApp.{Repo, UserManager.{User, Mail}}

invalid argument for alias, expected a compile time atom or alias, got: UserManager.{}(User, Mail)

Any thoughts on support for nested multi alias' ?

[José Valim]

You should break that into two aliases definitions. There is no plans for supporting nesting because I would consider that approach quite unreadable. :)

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José Valim

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José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

[moloney...@gmail.com]

Yes, makes sense. Clearer with two aliases alright.

alias MyApp.Repo
alias MyApp.UserManager.{User, Mail}

thanks.

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José Valim

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Skype: jv.ptec

Founder and Lead Developer