Use of macros with parentheses, square brackets, or curly braces
In our first example we used the println! macro with parentheses: println!() that made it look like a function call.
Rust allows us to use macros with square brackets or with curly braces.
In most cases people use regular parenthese, but for example the vec! macro is usually used with square brackets.
You can even leave spaces between the exclamation mark and the opening brace, but I don't think I have seen that. I'd probably avoid that.
The default formatting style of Rust is having no space when parenthese or square brackets are used and having a single space when curly brace is used.
fn main() { println!("Hello, world!"); println!["Hello, world!"]; println! {"Hello, world!"}; }