How do I avoid calling ".clone()" on same String in match multiple times? - regex

Question

Background:
I have some code (Rust) that finds (Regex) matches and assigns the found values to fields in a struct named Article (where all fields are of type String):
pub struct Article {
// user facing data
title: String,
category: String,
subcategory: String,
genre: String,
published: String,
estimated_read_time: String,
description: String,
tags: String,
keywords: String,
image: String,
artwork_credit: String,
// meta data
metas: String,
// location
path: String,
slug: String,
// file data
content: String
}
A regular expression ("//\- define (.*?): (.*?)\n") is used to extract comments from the article's template that define data for that article:
// iterate through HTML property pattern matches
for capture in re_define.captures_iter(&file_content as &str) {
// remove the declaration from the the HTML output
article_content = article_content.replace(&capture[0].to_string(), "");
// get the property value
let property_value: &String = &capture[2].to_string();
// determine what field to assign the property to and assign it
match capture[1].to_lowercase().as_str() {
"title" => article.title = property_value.clone(),
"category" => article.category = property_value.clone(),
"subcategory" => article.subcategory = property_value.clone(),
"genre" => article.genre = property_value.clone(),
"published" => article.published = property_value.clone(),
"estimated_read_time" => article.estimated_read_time = property_value.clone(),
"description" => article.description = property_value.clone(),
"tags" => article.tags = property_value.clone(),
"keywords" => article.keywords = property_value.clone(),
"image" => article.image = property_value.clone(),
unknown_property # _ => {
println!("Ignoring unknown property: {}", &unknown_property);
}
}
}
Note: article is an instance of Article.
Issue:
The code works but what I'm concerned about the following part:
"title" => article.title = property_value.clone(),
"category" => article.category = property_value.clone(),
"subcategory" => article.subcategory = property_value.clone(),
"genre" => article.genre = property_value.clone(),
"published" => article.published = property_value.clone(),
"estimated_read_time" => article.estimated_read_time = property_value.clone(),
"description" => article.description = property_value.clone(),
"tags" => article.tags = property_value.clone(),
"keywords" => article.keywords = property_value.clone(),
"image" => article.image = property_value.clone(),
It calls .clone() on the same String (property_value) for every match (10 matches per article template), for every article template (a couple dozen templates in total), and I don't think it's the most efficient way to do it.
Note: I'm not sure if match is cloning for non-matches.
What I tried:
I tried referencing the property_value String, but I got an error for each reference.
Error from IDE (VS Code):
mismatched types
expected struct `std::string::String`, found `&&std::string::String`
expected due to the type of this binding
try using a conversion method: `(`, `).to_string()`
Error from cargo check:
error[E0308]: mismatched types
--> src/article.rs:84:38
|
84 | "image" => article.image = &property_value,
| ------------- ^^^^^^^^^^^^^^^ expected struct `std::string::String`, found `&&std::string::String`
| |
| expected due to the type of this binding
|
help: try using a conversion method
|
84 | "image" => article.image = (&property_value).to_string(),
| + +++++++++++++
I did try using .to_string(), but I'm not sure if converting a String to the same type is the most efficient to do it either.
Question:
How do I avoid calling .clone() on property_value so many times?

Answer 1

Going by the types, you should just be able to drop the borrow in property_value and then you don't need the .clone()s.
let property_value: &String = &capture[2].to_string();
// change to
let property_value: String = capture[2].to_string();
// or just simply
let property_value = capture[2].to_string();
I'm assuming this was added as capture[2] returns a str (non-sized type) which would require the & but with to_string() it converts to the owned type String which is fine on it's own. This wont have any performance effect as to_string() copies anyway.