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Variants of await syntax for Rust

As the drive for async/await stabilization in Rust enters its final stretch, the latest discussion of await syntax has shown that the issue is as contentious as ever, with several firmly established camps. The lang team's excellent write up has narrowed down the choices to "prefix" and "postfix" categories, each of which contains several possible solutions, but so far the team hasn't reached consensus.

While there have been commendable attempts to illustrate the syntax with more substantial code excerpts, in general I feel that the discussion has been rather light on concrete, in-context examples. Even if a certain amount of abstractness is inevitable, in this case there is an existing corpus of working async code which can be adapted to various proposed syntaxes without much difficulty: components of Google's Fuchsia OS written in Rust.

I believe that there is value in seeing a language construct in the context of the rest of the source code. This repo starts with the source of an async-heavy utility and translates it to four variant syntaxes proposed by the lang team. More source files and await syntaxes can be added if there's interest: see the Contributing section.

Organization of the repo

The original source is copied from the tree at the commit 66e1924 of the master branch of the Fuchsia Garnet repo. This source uses the unstable await! macro. Translations to other syntaxes are in separate branches, named after the proposals in the lang team writeup:

  • prefix-mandatory: Prefix await with mandatory delimiters.

  • prefix-sugar: Prefix syntactic sugar for await+try.

  • postfix-field: Postfix field access syntax.

  • postfix-method: Postfix method syntax.

(The order of syntaxes in the above list follows the order in the writeup.)


If you notice an error in a translation, create a PR against the branch of the translation.

If you want to add a source file with at least two translations, first create a PR with the original against master, then the PRs for each translation against the corresponding branch. The original should be from the tree referenced in the Organization section.

If you want to contribute a translation to another syntax, open an issue and propose the creation of the appropriate branch. To keep the repo focused, please don't propose syntaxes which aren't in the lang team's writeup. Then, create a PR against the new branch.


The contents of this repo is covered by Google's Fuchsia license, which can be found in the LICENSE file.


Illustration of Rust await syntax alternatives







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