this post was submitted on 23 Sep 2024
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Rust Programming

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Which of these code styles do you find preferable?

First option using mut with constructor in the beginning:

  let mut post_form = PostInsertForm::new(
    data.name.trim().to_string(),
    local_user_view.person.id,
    data.community_id,
  );
  post_form.url = url.map(Into::into);
  post_form.body = body;
  post_form.alt_text = data.alt_text.clone();
  post_form.nsfw = data.nsfw;
  post_form.language_id = language_id;

Second option without mut and constructor at the end:

  let post_form = PostInsertForm {
    url: url.map(Into::into),
    body,
    alt_text: data.alt_text.clone(),
    nsfw: data.nsfw,
    language_id,
    ..PostInsertForm::new(
      data.name.trim().to_string(),
      local_user_view.person.id,
      data.community_id,
    )
  };

You can see the full PR here: https://github.com/LemmyNet/lemmy/pull/5037/files

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[–] [email protected] 0 points 1 month ago (1 children)

@[email protected] @[email protected] @[email protected] Thanks for the feedback! Personally I prefer the first option, but based on your comments I will merge the PR with the second option.

[–] [email protected] 0 points 1 month ago (2 children)

If you're ever forced to do something the second way, you can also wrap it in braces, that way you end up with an immutable value again:

let app = {
  let mut app = ...
  ...
  app
};
[–] [email protected] 0 points 1 month ago (1 children)

Why not just a let app = app; line after the let mut app = ...; one?

[–] [email protected] 0 points 1 month ago (1 children)

A scope groups the initialization visually together, while adding the let app = app; feels like it just adds clutter - I'd probably just leave it mut in that case.

[–] [email protected] 0 points 1 month ago

Rebinding with and without mut is a known and encouraged pattern in rust. Leaving things as mut longer than necessary is not.

[–] [email protected] 0 points 1 month ago (1 children)

Thats even more verbose so the second option is better.

[–] [email protected] 0 points 1 month ago (1 children)

Yeah if you have the second option, use it, but if the struct has private fields it won't work.

[–] [email protected] 0 points 1 month ago (1 children)

The first one won't work either for private fields.

[–] [email protected] 0 points 1 month ago (1 children)

You can have setters that set private fields, there are also sometimes structs with mixed private and public fields

[–] [email protected] 0 points 1 month ago (1 children)

But why not use a proper builder pattern in that case?

[–] [email protected] 0 points 1 month ago

Because you don't control third party libraries