fns that should be in Rust `core` library (wait, they are! https://doc.rust-lang.org/std/option/enum.Option.html#method.filter)

conditional_identity.rs

#![no_std]

/// if `cond` is `true`, then `identity(x)`
///
/// if `cond` is `false` then `drop(x)`
pub fn cond_ident<T>(cond: bool, x: T) -> Option<T> {
    if cond {
        Some(x)
    } else {
        None
    }
}

/// if `pred` returns `true`, then `identity(x)`
///
/// if `pred` returns `false` then `drop(x)`
pub fn pred_ident<F: FnOnce(&T) -> bool, T>(pred: F, x: T) -> Option<T> {
    if pred(&x) {
        Some(x)
    } else {
        None
    }
} // should it be `impl FnOnce(&T) -> bool`?
// API would be "less flexible",
// but `Option::is_some_and` doesn't seem to care