Making Rust Strings is silly

_posts/2022-10-28-rust-strings.md

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+---
+layout: post
+title: The fastest way to make Rust Strings
+tags:
+- rust
+- software
+- software development
+---
+
+A friend of mine learning how to code with Python was complaining about the
+myth that "there's a Pythonic way" to do things. The "one true way" concept
+wasn't ever taken seriously in Python, not even by the standard library.
+Practically speaking, it's impossible _not_ to have multiple ways to accomplish
+the same outcome in a robust programming language's standard library. This
+_flexibility_ jumped out at me while hacking on some Rust code lately: how many
+ways can you turn `str`
+into `String`?
+
+In Rust `"this thing"` is a [primitive `str`
+type](https://doc.rust-lang.org/std/primitive.str.html#) and will have the
+`&'static` lifetime. Without diving into lifetimes and how Rust ownership
+works, this is basically read-only memory that exists for the duration of the
+program. They're _static_ and you can't do much with it. In _most_ APIs you'll
+need the [`String`
+type](https://doc.rust-lang.org/std/string/struct.String.html), which will give
+you an allocated bit of data you can play around with.
+
+Without much effort I came up with five different ways that I have written Rust
+code to perform this conversion:
+
+1. `String::from("The boring way")`
+2. `"Using a trait".into()`
+3. `"This is actually a trait too".to_string()`
+4. `"Lol, this is also a trait".to_owned()`
+5. `format!("Wake up and choose violence")`
+
+---
+If you have some other nifty ways to create `String`s, let me know on
+[Twitter](https://twitter.com) or via email (`rtyler@` this domain)!
+
+
+---
+
+
+But which is the most fastest?! I wrote the following very important, and very serious microbenchmarking code:
+
+```rust
+use microbench::{self, Options};
+
+fn into_trait() {
+    let _s: String = "Rust is cool!".into();
+}
+
+fn to_string() {
+    let _s: String = "Rust is cool!".to_string();
+}
+
+fn format() {
+    let _s: String = format!("Rust is cool!");
+}
+
+fn owned() {
+    let _s: String = "Rust is cool!".to_owned();
+}
+
+fn string_from() {
+    let _s: String = String::from("Rust is cool!");
+}
+
+fn main() {
+    let options = Options::default();
+    microbench::bench(&options, "String::from!", || string_from());
+    microbench::bench(&options, "Into<String>", || into_trait());
+    microbench::bench(&options, "ToString<str>", || to_string());
+    microbench::bench(&options, "ToOwned<str>", || owned());
+    microbench::bench(&options, "format!", || format());
+}
+```
+
+I compiled the program with `rustc` version 1.63.0 and after running some truly
+rigorous and scientific tests on my workstation, I am thrilled to share the results:
+
+```
+❯ cargo run
+   Compiling rust-strings-are-silly v0.1.0 (/home/tyler/source/github/rtyler/rust-strings-are-silly)
+    Finished dev [unoptimized + debuginfo] target(s) in 0.25s
+     Running `target/debug/rust-strings-are-silly`
+String::from! (5.0s) ...                 278.552 ns/iter (0.991 R²)
+Into<String> (5.0s) ...                  286.293 ns/iter (0.983 R²)
+ToString<str> (5.0s) ...                 292.736 ns/iter (0.987 R²)
+ToOwned<str> (5.0s) ...                  290.276 ns/iter (0.985 R²)
+format! (5.0s) ...                       300.144 ns/iter (0.995 R²)
+```
+
+
+**HOW INTERESTING!**
+
+Well, not really.
+
+Microbenchmarking like this has **lots** of flaws,
+especially when sampling on a single machine running many other concurrent
+processes. After executing the tool a few times, one common pattern that I did see was that
+the `format!` macro is consistently the slowest way to create `String`s. In
+fact `cargo clippy` will complain about you using in this way, not because it's
+slow, but because it's a "useless use of `format!`", which I can agree with! :)
+
+
+Choosing between the rest of them probably is nothing more than a style choice
+of the developers working on any given Rust project. With these types of things
+it's typically best to adopt one consistent way of doing things _within the
+codebase_ to improve readability, but they're all functionally equivalent..
+
+In Rust there's no "one true way" to create a `String`, but my personal
+preference is `.into()` for no other reason than it is the fewest
+characters to type!