6mo ago

Which code style to initialize structs?

Which of these code styles do you find preferable?

First option using mut with constructor in the beginning:

 rust

    
  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:

 rust

    
  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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23 comments

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

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

23 comments