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Which code style to initialize structs? (lemmy.ml)

submitted 1 month ago by [email protected] to c/[email protected]

23 comments fedilink hide all child comments

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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[–] livingcoder 2 points 1 month ago* (last edited 1 month ago) (2 children)

I prefer to encapsulate a mutable reference to the instance in a scope.

let post_form = {
    let mut post_form = PostInsertForm::new(
        // your constructor arguments
    );
    post_form.some_mutating_method(
        // mutation arguments
    );
    post_form
};

This way you're left with an immutable instance and you encapsulate all of the logic needed to setup the instance in one place.

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

@livingcoder @nutomic that's a nice one. Had never thought of it. But I'd just use the builder pattern.

[–] livingcoder 2 points 1 month ago* (last edited 1 month ago)

Even if you were using the builder pattern, this maintains the immutable variable in the parent scope while you use the mutable variable's builder pattern methods (basically exactly as my example demonstrates) in the inner scope.

edit: Oh, I think you mean you would chain the builder pattern calls and assign it to an immutable variable. Sure, that makes sense if you own the struct.