Crabrix

Rust Foundations · 10 min · free with an account

Hello, Rust

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A small Rust program gives you the whole development loop: write a function, let the compiler check it, run it, and inspect what appeared on stdout.

Core idea

Execution begins in fn main(). println! is a compile-time-checked macro that writes a formatted line to stdout when the program runs.

Start with the idea

A Rust executable begins in fn main(). The braces enclose the statements that run when the program starts. In the example, name is a string slice, and println!("Hello, {name}!") uses it to build a line of text. The exclamation mark matters: println! is a macro, not an ordinary function call. It expands while the program is compiled, so the compiler can check the format string and its arguments before anything runs. If a placeholder is missing an argument, you see a diagnostic instead of a half-working program.

Follow the diagram from left to right: source code, a successful compile-time check, then terminal output. The compiler’s messages are not the same as your program’s stdout. A clean build can still produce no output if there is no print call; a failed build cannot run this new version at all. When you change the greeting, predict the exact line you expect before tapping Run.

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