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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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.
@livingcoder @nutomic that’s a nice one. Had never thought of it. But I’d just use the builder pattern.
Defo the second one, the first is weird imo
100% the second one. It’s the idiomatic way to do this in Rust, and it leaves you with an immutable object.
I personally like to move the short declarations together (i.e. body down with language_id (or both at the top)) but that’s a minor quibble.
@DemocratPostingSucks@lemm.ee @Deebster@programming.dev @al4s@feddit.org Thanks for the feedback! Personally I prefer the first option, but based on your comments I will merge the PR with the second option.
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 };Why not just a
let app = app;line after thelet mut app = ...;one?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.Rebinding with and without
mutis a known and encouraged pattern in rust. Leaving things asmutlonger than necessary is not.
Thats even more verbose so the second option is better.
Yeah if you have the second option, use it, but if the struct has private fields it won’t work.
The first one won’t work either for private fields.
You can have setters that set private fields, there are also sometimes structs with mixed private and public fields
But why not use a proper builder pattern in that case?
Because you don’t control third party libraries
also adding my vote for the second one
Neither.
- make
new()give you a fully valid and usable struct value. - or use a builder (you can call it something else like Partial/Incomplete/whatever) struct so you can’t accidentally do anything without a fully initialized value.
Maybe you should also use substructs that hold some of the info.
- make
Second one if a constructor or a builder is not an option. 1 is out of the question.
Why are the Lemmy devs asking for this though?
To decide if I should merge the linked PR or not (I did merge it).
Definitely the second one.
- It avoids Mut
- It makes clear that the initialization is over at the end of of the statement. The first option invites people to change some more properties hundreds of lines down where you won’t see them.
