Idiomatic Rust Snippets

What is the purpose of ![no_std]?

The #![no_std] attribute in Rust is used to indicate that a crate does not use the Rust standard library (std). Instead, it relies on the core library (core), which is a subset of the standard library and is available in environments where the full standard library is not available, such as embedded systems or operating system kernels.

Purpose of #![no_std]

Embedded Systems: Many embedded systems do not have the resources to support the full standard library.
Operating System Development: When writing an operating system, you often need to avoid dependencies on the standard library.
Custom Environments: Any environment where the standard library is not available or not desired.

Here’s an example of how you might use #![no_std] in a Rust crate:

#![no_std]

extern crate core;

use core::fmt;

struct MyStruct;

impl fmt::Display for MyStruct {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Hello, no_std!")
    }
}

fn main() {
    let my_struct = MyStruct;
    println!("{}", my_struct); // This will not work because println! is part of std
}

Key Points

No Standard Library: The crate does not link to the standard library.
Use core: You can use the core library, which provides essential functionalities like Option, Result, and basic traits.
Limited Functionality: Without the standard library, you lose access to many features like heap allocation, file I/O, and threading.

Common Use Cases

Embedded Development: Writing firmware for microcontrollers.
Operating System Kernels: Developing low-level system software.
WASM (WebAssembly): Targeting WebAssembly where the standard library is not fully supported.