falseKeyword

Explanation

false is the boolean literal for a false value, of type bool. Like true, it is both a reserved keyword and a complete literal expression.

See true for the surrounding notes on bool as a distinct, non-numeric type with no implicit conversions.

Usage examples

The `false` boolean literal

let done: bool = false; // <- `false` is the boolean literal for a false value

Validating input

A struct of feature flags implements Default so any new, unreleased feature starts disabled unless explicitly opted into — false is the conservative default for a flag that shouldn't be on until someone turns it on.

struct FeatureFlags {
    enable_beta_ui: bool,
}

impl Default for FeatureFlags {
    fn default() -> Self {
        FeatureFlags {
            enable_beta_ui: false, // <- unreleased features default to `false` until explicitly opted in
        }
    }
}

Defaulting risky or unfinished behavior to false means a missing configuration value fails closed rather than open. Making that the Default also lines up with the API Guidelines' C-COMMON-TRAITS, which recommends types eagerly implement Default. See true for the fuller treatment of bool literals.

Explanation

Embedded support: Full

As with true, there's no genuine embedded-specific angle to false — it's the same core primitive literal, identical under #![no_std]. It's worth naming plainly rather than manufacturing a distinction: the only embedded-flavored thing to say is what a false typically represents in firmware — an interrupt flag that hasn't fired yet, or a peripheral not yet ready.

Usage examples

A completion flag that starts false until an interrupt fires

let mut dma_transfer_complete = false; // <- `false` is the initial state before the DMA interrupt sets it

fn on_dma_complete(flag: &mut bool) {
    *flag = true;
}