MutStr

MutStr is a good solution if you want to reduce memory consumption for e.g. hash tables like <String, String> and need something more efficient than Box<str> because you have to change the data at runtime.

• MutStr uses 16 bytes.
• String uses 24 bytes.

If you don't change the data at runtime, use Box<str>. If you prefer speed when adding new data, choose String. If you need low memory consumption and changeable data, choose MutStr.

What does "... more efficient than Box<str> ..." mean?

The inner value of Box<str> cannot be changed, for this reason, the old Box<str> has to be replaced with a new allocated Box<str>, which is more inefficient than reallocate the inner value. See our benchmarks

Benchmark results

This benchmark was updated at January 13th, 2024 and can be found here.

create_box                   28 ns/iter (+/- 3)
create_string                28 ns/iter (+/- 1)
create_mutstr                28 ns/iter (+/- 0)
replace_box_data             104 ns/iter (+/- 3)
replace_string_data          85 ns/iter (+/- 7)
replace_mutstr_data          82 ns/iter (+/- 1)

Example

You can easily add new values or remove existing ones with MutStr.

use mutstr::mutstr;

fn main() {
  let mut result = mutstr::from("hello");
  result += " my friend"; // Add -> " my friend"
  result -= " friend"; // Remove -> " friend"
  assert_eq!(result.as_str(), "hello my");
  
  result.push(" friend friend friend"); // Add -> " friend friend friend"
  result -= (2, " friend"); // Remove(2 times) -> " friend"
  assert_eq!(result.as_str(), "hello my friend");
  
  result += String::from(" :)"); // Add -> " :)"
  assert_eq!(result.as_str(), "hello my friend :)");
}

Example

You can easily get a &str from a MutStr like you would with String.

use mutstr::mutstr;

fn main() {
  let first = String::from("hello friend");
  let first_str = &*first; // String as `&str`
  let second = mutstr::from("hello friend");
  let second_str = &*second; // MutStr as `&str`
  assert_eq!(first_str, second_str);
}

Example

You can easily use MutStr in hash tables and vectors, like you can with Box<str>.

use std::collections::HashMap;
use mutstr::mutstr;

fn main() {
  let mut result = HashMap::<Box<str>, mutstr>::new();
  result.insert(Box::from("hello"), mutstr::from("friend"));
  
  let value = result.get_mut("hello").unwrap();
  *value += " :)";
  
  assert_eq!(value.as_str(), "friend :)");
}