1219-use-group-as.md

• Feature Name: use_group_as
• Start Date: 2015-02-15
• RFC PR: rust-lang/rfcs#1219
• Rust Issue: rust-lang/rust#27578

Summary

Allow renaming imports when importing a group of symbols from a module.

use std::io::{
    Error as IoError,
    Result as IoResult,
    Read,
    Write
}

Motivation

The current design requires the above example to be written like this:

use std::io::Error as IoError;
use std::io::Result as IoResult;
use std::io::{Read, Write};

It's unfortunate to duplicate use std::io:: on the 3 lines, and the proposed example feels logical, and something you reach for in this instance, without knowing for sure if it worked.

Detailed design

The current grammar for use statements is something like:

  use_decl : "pub" ? "use" [ path "as" ident
                            | path_glob ] ;

  path_glob : ident [ "::" [ path_glob
                            | '*' ] ] ?
            | '{' path_item [ ',' path_item ] * '}' ;

  path_item : ident | "self" ;

This RFC proposes changing the grammar to something like:

  use_decl : "pub" ? "use" [ path [ "as" ident ] ?
                            | path_glob ] ;

  path_glob : ident [ "::" [ path_glob
                            | '*' ] ] ?
            | '{' path_item [ ',' path_item ] * '}' ;

  path_item : ident [ "as" ident] ?
            | "self" [ "as" ident];

The "as" ident part is optional in each location, and if omitted, it is expanded to alias to the same name, e.g. use foo::{bar} expands to use foo::{bar as bar}.

This includes being able to rename self, such as use std::io::{self as stdio, Result as IoResult};.

Drawbacks

Alternatives

Unresolved Questions