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constify Option methods #143967

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Jul 18, 2025
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constify Option methods #143967

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137 changes: 97 additions & 40 deletions library/core/src/option.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -577,6 +577,7 @@
#![stable(feature = "rust1", since = "1.0.0")]

use crate::iter::{self, FusedIterator, TrustedLen};
use crate::marker::Destruct;
use crate::ops::{self, ControlFlow, Deref, DerefMut};
use crate::panicking::{panic, panic_display};
use crate::pin::Pin;
Expand Down Expand Up @@ -649,7 +650,8 @@ impl<T> Option<T> {
#[must_use]
#[inline]
#[stable(feature = "is_some_and", since = "1.70.0")]
pub fn is_some_and(self, f: impl FnOnce(T) -> bool) -> bool {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn is_some_and(self, f: impl ~const FnOnce(T) -> bool + ~const Destruct) -> bool {
match self {
None => false,
Some(x) => f(x),
Expand Down Expand Up @@ -697,7 +699,8 @@ impl<T> Option<T> {
#[must_use]
#[inline]
#[stable(feature = "is_none_or", since = "1.82.0")]
pub fn is_none_or(self, f: impl FnOnce(T) -> bool) -> bool {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn is_none_or(self, f: impl ~const FnOnce(T) -> bool + ~const Destruct) -> bool {
match self {
None => true,
Some(x) => f(x),
Expand Down Expand Up @@ -1023,7 +1026,12 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn unwrap_or(self, default: T) -> T {
#[rustc_allow_const_fn_unstable(const_precise_live_drops)]
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn unwrap_or(self, default: T) -> T
where
T: ~const Destruct,
{
match self {
Some(x) => x,
None => default,
Expand All @@ -1042,9 +1050,10 @@ impl<T> Option<T> {
#[inline]
#[track_caller]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn unwrap_or_else<F>(self, f: F) -> T
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn unwrap_or_else<F>(self, f: F) -> T
where
F: FnOnce() -> T,
F: ~const FnOnce() -> T + ~const Destruct,
{
match self {
Some(x) => x,
Expand Down Expand Up @@ -1073,9 +1082,10 @@ impl<T> Option<T> {
/// [`FromStr`]: crate::str::FromStr
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn unwrap_or_default(self) -> T
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn unwrap_or_default(self) -> T
where
T: Default,
T: ~const Default,
{
match self {
Some(x) => x,
Expand Down Expand Up @@ -1139,9 +1149,10 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn map<U, F>(self, f: F) -> Option<U>
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn map<U, F>(self, f: F) -> Option<U>
where
F: FnOnce(T) -> U,
F: ~const FnOnce(T) -> U + ~const Destruct,
{
match self {
Some(x) => Some(f(x)),
Expand Down Expand Up @@ -1169,7 +1180,11 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "result_option_inspect", since = "1.76.0")]
pub fn inspect<F: FnOnce(&T)>(self, f: F) -> Self {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn inspect<F>(self, f: F) -> Self
where
F: ~const FnOnce(&T) + ~const Destruct,
{
if let Some(ref x) = self {
f(x);
}
Expand Down Expand Up @@ -1198,9 +1213,11 @@ impl<T> Option<T> {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use = "if you don't need the returned value, use `if let` instead"]
pub fn map_or<U, F>(self, default: U, f: F) -> U
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn map_or<U, F>(self, default: U, f: F) -> U
where
F: FnOnce(T) -> U,
F: ~const FnOnce(T) -> U + ~const Destruct,
U: ~const Destruct,
{
match self {
Some(t) => f(t),
Expand Down Expand Up @@ -1243,10 +1260,11 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn map_or_else<U, D, F>(self, default: D, f: F) -> U
where
D: FnOnce() -> U,
F: FnOnce(T) -> U,
D: ~const FnOnce() -> U + ~const Destruct,
F: ~const FnOnce(T) -> U + ~const Destruct,
{
match self {
Some(t) => f(t),
Expand All @@ -1273,10 +1291,11 @@ impl<T> Option<T> {
/// [default value]: Default::default
#[inline]
#[unstable(feature = "result_option_map_or_default", issue = "138099")]
pub fn map_or_default<U, F>(self, f: F) -> U
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn map_or_default<U, F>(self, f: F) -> U
where
U: Default,
F: FnOnce(T) -> U,
U: ~const Default,
F: ~const FnOnce(T) -> U + ~const Destruct,
{
match self {
Some(t) => f(t),
Expand Down Expand Up @@ -1307,7 +1326,8 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn ok_or<E>(self, err: E) -> Result<T, E> {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn ok_or<E: ~const Destruct>(self, err: E) -> Result<T, E> {
match self {
Some(v) => Ok(v),
None => Err(err),
Expand All @@ -1332,9 +1352,10 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn ok_or_else<E, F>(self, err: F) -> Result<T, E>
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn ok_or_else<E, F>(self, err: F) -> Result<T, E>
where
F: FnOnce() -> E,
F: ~const FnOnce() -> E + ~const Destruct,
{
match self {
Some(v) => Ok(v),
Expand Down Expand Up @@ -1463,7 +1484,12 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn and<U>(self, optb: Option<U>) -> Option<U> {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn and<U>(self, optb: Option<U>) -> Option<U>
where
T: ~const Destruct,
U: ~const Destruct,
{
match self {
Some(_) => optb,
None => None,
Expand Down Expand Up @@ -1502,9 +1528,10 @@ impl<T> Option<T> {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_confusables("flat_map", "flatmap")]
pub fn and_then<U, F>(self, f: F) -> Option<U>
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn and_then<U, F>(self, f: F) -> Option<U>
where
F: FnOnce(T) -> Option<U>,
F: ~const FnOnce(T) -> Option<U> + ~const Destruct,
{
match self {
Some(x) => f(x),
Expand Down Expand Up @@ -1538,9 +1565,11 @@ impl<T> Option<T> {
/// [`Some(t)`]: Some
#[inline]
#[stable(feature = "option_filter", since = "1.27.0")]
pub fn filter<P>(self, predicate: P) -> Self
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn filter<P>(self, predicate: P) -> Self
where
P: FnOnce(&T) -> bool,
P: ~const FnOnce(&T) -> bool + ~const Destruct,
T: ~const Destruct,
{
if let Some(x) = self {
if predicate(&x) {
Expand Down Expand Up @@ -1579,7 +1608,11 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn or(self, optb: Option<T>) -> Option<T> {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn or(self, optb: Option<T>) -> Option<T>
where
T: ~const Destruct,
{
match self {
x @ Some(_) => x,
None => optb,
Expand All @@ -1601,9 +1634,13 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn or_else<F>(self, f: F) -> Option<T>
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn or_else<F>(self, f: F) -> Option<T>
where
F: FnOnce() -> Option<T>,
F: ~const FnOnce() -> Option<T> + ~const Destruct,
//FIXME(const_hack): this `T: ~const Destruct` is unnecessary, but even precise live drops can't tell
// no value of type `T` gets dropped here
Comment on lines +1641 to +1642
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I have a feeling this will nerdsnipe me hard.

Here's how code is currently generated

#![feature(const_destruct)]
#![feature(const_trait_impl)]

use std::marker::Destruct;

pub const fn opt_or_else<T, F>(this: Option<T>, f: F) -> Option<T>
where
    F: ~const Destruct + ~const FnOnce() -> Option<T>,
    T: ~const Destruct
{
    match this {
        x @ Some(_) => x,
        None => f()
    }
}
// MIR FOR CTFE
fn opt_or_else(_1: Option<T>, _2: F) -> Option<T> {
    debug this => _1;
    debug f => _2;
    let mut _0: std::option::Option<T>;
    let mut _3: isize;
    let _4: std::option::Option<T>;
    let mut _5: F;
    let mut _6: ();
    let mut _7: bool;
    let mut _8: bool;
    scope 1 {
        debug x => _4;
    }

    bb0: {
        _8 = const false;
        _7 = const false;
        _8 = const true;
        _7 = const true;
        _3 = discriminant(_1);
        switchInt(move _3) -> [0: bb2, 1: bb3, otherwise: bb1];
    }

    bb1: {
        unreachable;
    }

    bb2: {
        StorageLive(_5);
        _7 = const false;
        _5 = move _2;
        StorageLive(_6);
        _6 = ();
        ConstEvalCounter;
        _0 = <F as FnOnce<()>>::call_once(move _5, move _6) -> [return: bb4, unwind: bb12];
    }

    bb3: {
        StorageLive(_4);
        _8 = const false;
        _4 = move _1;
        _0 = move _4;
        StorageDead(_4);
        goto -> bb9;
    }

    bb4: {
        StorageDead(_6);
        StorageDead(_5);
        goto -> bb9;
    }

    bb5: {
        switchInt(copy _8) -> [0: bb6, otherwise: bb10];
    }

    bb6: {
        return;
    }

    bb7 (cleanup): {
        resume;
    }

    bb8: {
        drop(_2) -> [return: bb5, unwind: bb12];
    }

    bb9: {
        switchInt(copy _7) -> [0: bb5, otherwise: bb8];
    }

    bb10: {
        drop(_1) -> [return: bb6, unwind: bb7];
    }

    bb11 (cleanup): {
        drop(_1) -> [return: bb7, unwind terminate(cleanup)];
    }

    bb12 (cleanup): {
        switchInt(copy _8) -> [0: bb7, otherwise: bb11];
    }
}

looks like it tries to drop self at the None arm, which is just weird.

T: ~const Destruct,
{
match self {
x @ Some(_) => x,
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This pattern was introduced in #116481 because it optimizes better.

Expand Down Expand Up @@ -1634,7 +1671,11 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "option_xor", since = "1.37.0")]
pub fn xor(self, optb: Option<T>) -> Option<T> {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn xor(self, optb: Option<T>) -> Option<T>
where
T: ~const Destruct,
{
match (self, optb) {
(a @ Some(_), None) => a,
(None, b @ Some(_)) => b,
Expand Down Expand Up @@ -1668,7 +1709,11 @@ impl<T> Option<T> {
#[must_use = "if you intended to set a value, consider assignment instead"]
#[inline]
#[stable(feature = "option_insert", since = "1.53.0")]
pub fn insert(&mut self, value: T) -> &mut T {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn insert(&mut self, value: T) -> &mut T
where
T: ~const Destruct,
{
*self = Some(value);

// SAFETY: the code above just filled the option
Expand Down Expand Up @@ -1720,9 +1765,10 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "option_get_or_insert_default", since = "1.83.0")]
pub fn get_or_insert_default(&mut self) -> &mut T
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn get_or_insert_default(&mut self) -> &mut T
where
T: Default,
T: ~const Default + ~const Destruct,
{
self.get_or_insert_with(T::default)
}
Expand All @@ -1746,9 +1792,11 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "option_entry", since = "1.20.0")]
pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut T
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn get_or_insert_with<F>(&mut self, f: F) -> &mut T
where
F: FnOnce() -> T,
F: ~const FnOnce() -> T + ~const Destruct,
T: ~const Destruct,
{
if let None = self {
*self = Some(f());
Expand Down Expand Up @@ -1812,9 +1860,10 @@ impl<T> Option<T> {
/// ```
#[inline]
#[stable(feature = "option_take_if", since = "1.80.0")]
pub fn take_if<P>(&mut self, predicate: P) -> Option<T>
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn take_if<P>(&mut self, predicate: P) -> Option<T>
where
P: FnOnce(&mut T) -> bool,
P: ~const FnOnce(&mut T) -> bool + ~const Destruct,
{
if self.as_mut().map_or(false, predicate) { self.take() } else { None }
}
Expand Down Expand Up @@ -1859,7 +1908,12 @@ impl<T> Option<T> {
/// assert_eq!(x.zip(z), None);
/// ```
#[stable(feature = "option_zip_option", since = "1.46.0")]
pub fn zip<U>(self, other: Option<U>) -> Option<(T, U)> {
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn zip<U>(self, other: Option<U>) -> Option<(T, U)>
where
T: ~const Destruct,
U: ~const Destruct,
{
match (self, other) {
(Some(a), Some(b)) => Some((a, b)),
_ => None,
Expand Down Expand Up @@ -1895,9 +1949,12 @@ impl<T> Option<T> {
/// assert_eq!(x.zip_with(None, Point::new), None);
/// ```
#[unstable(feature = "option_zip", issue = "70086")]
pub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>
#[rustc_const_unstable(feature = "const_option_ops", issue = "143956")]
pub const fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>
where
F: FnOnce(T, U) -> R,
F: ~const FnOnce(T, U) -> R + ~const Destruct,
T: ~const Destruct,
U: ~const Destruct,
{
match (self, other) {
(Some(a), Some(b)) => Some(f(a, b)),
Expand Down
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