Macro std::cfg

macro cfg($s) { ... }

source

Returns the value of a configuration flag during compilation.

This can be used as an alternative to #[cfg] attributes. The difference is that cfg! can be used in any expression position, while #[cfg] can only be used on statements and items.

Example

use std::cfg;
use std::time::Duration;
use std::thread::sleep;

when cfg!("debug") {
    sleep(Duration::from_millis(100));
    println!("program was built in debug mode, that's why it's so slow ;)");
} else {
    println!("program was built in release mode and is blazing fast!");
}
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