|
| 1 | +//! A custom LazyLock+Cow suitable for holding borrowed, owned or lazy data. |
| 2 | +
|
| 3 | +use std::borrow::{Borrow, Cow}; |
| 4 | +use std::fmt::{Debug, Display}; |
| 5 | +use std::ops::Deref; |
| 6 | +use std::sync::LazyLock; |
| 7 | + |
| 8 | +enum MaybeLazyInner<T: 'static + ToOwned + ?Sized, F> { |
| 9 | + Lazy(LazyLock<T::Owned, F>), |
| 10 | + Cow(Cow<'static, T>), |
| 11 | +} |
| 12 | + |
| 13 | +/// A custom LazyLock+Cow suitable for holding borrowed, owned or lazy data. |
| 14 | +/// |
| 15 | +/// Technically this structure has 3 states: borrowed, owned and lazy |
| 16 | +/// They can all be constructed from the [`MaybeLazy::borrowed`], [`MaybeLazy::owned`] and |
| 17 | +/// [`MaybeLazy::lazy`] methods. |
| 18 | +#[repr(transparent)] |
| 19 | +pub struct MaybeLazy<T: 'static + ToOwned + ?Sized, F = fn() -> <T as ToOwned>::Owned> { |
| 20 | + // Inner state. |
| 21 | + // |
| 22 | + // Not to be inlined since we may want in the future to |
| 23 | + // make this struct usable to statics and we might need to |
| 24 | + // workaround const-eval limitation (particulary around drop). |
| 25 | + inner: MaybeLazyInner<T, F>, |
| 26 | +} |
| 27 | + |
| 28 | +impl<T: 'static + ?Sized + ToOwned, F: FnOnce() -> T::Owned> MaybeLazy<T, F> { |
| 29 | + /// Create a [`MaybeLazy`] from an borrowed `T`. |
| 30 | + #[inline] |
| 31 | + pub const fn borrowed(a: &'static T) -> Self { |
| 32 | + MaybeLazy { inner: MaybeLazyInner::Cow(Cow::Borrowed(a)) } |
| 33 | + } |
| 34 | + |
| 35 | + /// Create a [`MaybeLazy`] from an borrowed `T`. |
| 36 | + #[inline] |
| 37 | + pub const fn owned(a: T::Owned) -> Self { |
| 38 | + MaybeLazy { inner: MaybeLazyInner::Cow(Cow::Owned(a)) } |
| 39 | + } |
| 40 | + |
| 41 | + /// Create a [`MaybeLazy`] from a function-able `F`. |
| 42 | + #[inline] |
| 43 | + pub const fn lazied(f: F) -> Self { |
| 44 | + MaybeLazy { inner: MaybeLazyInner::Lazy(LazyLock::new(f)) } |
| 45 | + } |
| 46 | +} |
| 47 | + |
| 48 | +impl<T: 'static + ?Sized + ToOwned> MaybeLazy<T> { |
| 49 | + /// Create a [`MaybeLazy`] from a function pointer. |
| 50 | + #[inline] |
| 51 | + pub const fn lazy(a: fn() -> T::Owned) -> Self { |
| 52 | + Self::lazied(a) |
| 53 | + } |
| 54 | +} |
| 55 | + |
| 56 | +impl<T: 'static + ?Sized + ToOwned<Owned: Clone>, F: FnOnce() -> T::Owned> Clone |
| 57 | + for MaybeLazy<T, F> |
| 58 | +{ |
| 59 | + #[inline] |
| 60 | + fn clone(&self) -> Self { |
| 61 | + MaybeLazy { |
| 62 | + inner: MaybeLazyInner::Cow(match &self.inner { |
| 63 | + MaybeLazyInner::Lazy(f) => Cow::Owned((*f).to_owned()), |
| 64 | + MaybeLazyInner::Cow(c) => c.clone(), |
| 65 | + }), |
| 66 | + } |
| 67 | + } |
| 68 | +} |
| 69 | + |
| 70 | +impl<T: 'static + ?Sized + ToOwned<Owned: Default>, F: FnOnce() -> T::Owned> Default |
| 71 | + for MaybeLazy<T, F> |
| 72 | +{ |
| 73 | + #[inline] |
| 74 | + fn default() -> MaybeLazy<T, F> { |
| 75 | + MaybeLazy::owned(T::Owned::default()) |
| 76 | + } |
| 77 | +} |
| 78 | + |
| 79 | +// `Debug`, `Display` and other traits below are implemented in terms of this `Deref` |
| 80 | +impl<T: 'static + ?Sized + ToOwned<Owned: Borrow<T>>, F: FnOnce() -> T::Owned> Deref |
| 81 | + for MaybeLazy<T, F> |
| 82 | +{ |
| 83 | + type Target = T; |
| 84 | + |
| 85 | + #[inline] |
| 86 | + fn deref(&self) -> &T { |
| 87 | + match &self.inner { |
| 88 | + MaybeLazyInner::Lazy(f) => (&**f).borrow(), |
| 89 | + MaybeLazyInner::Cow(c) => &*c, |
| 90 | + } |
| 91 | + } |
| 92 | +} |
| 93 | + |
| 94 | +impl<T: 'static + ?Sized + ToOwned<Owned: Debug> + Debug, F: FnOnce() -> T::Owned> Debug |
| 95 | + for MaybeLazy<T, F> |
| 96 | +{ |
| 97 | + #[inline] |
| 98 | + fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { |
| 99 | + Debug::fmt(&**self, fmt) |
| 100 | + } |
| 101 | +} |
| 102 | + |
| 103 | +impl<T: 'static + ?Sized + ToOwned<Owned: Display> + Display, F: FnOnce() -> T::Owned> Display |
| 104 | + for MaybeLazy<T, F> |
| 105 | +{ |
| 106 | + #[inline] |
| 107 | + fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { |
| 108 | + Display::fmt(&**self, fmt) |
| 109 | + } |
| 110 | +} |
| 111 | + |
| 112 | +impl<T: 'static + ?Sized + ToOwned, F: FnOnce() -> T::Owned> AsRef<T> for MaybeLazy<T, F> { |
| 113 | + #[inline] |
| 114 | + fn as_ref(&self) -> &T { |
| 115 | + &**self |
| 116 | + } |
| 117 | +} |
| 118 | + |
| 119 | +impl< |
| 120 | + T1: ?Sized + PartialEq<T2> + ToOwned, |
| 121 | + T2: ?Sized + ToOwned, |
| 122 | + F1: FnOnce() -> T1::Owned, |
| 123 | + F2: FnOnce() -> T2::Owned, |
| 124 | +> PartialEq<MaybeLazy<T2, F2>> for MaybeLazy<T1, F1> |
| 125 | +{ |
| 126 | + #[inline] |
| 127 | + fn eq(&self, other: &MaybeLazy<T2, F2>) -> bool { |
| 128 | + PartialEq::eq(&**self, &**other) |
| 129 | + } |
| 130 | +} |
| 131 | + |
| 132 | +impl<F: FnOnce() -> String> PartialEq<&str> for MaybeLazy<str, F> { |
| 133 | + #[inline] |
| 134 | + fn eq(&self, other: &&str) -> bool { |
| 135 | + &**self == *other |
| 136 | + } |
| 137 | +} |
| 138 | + |
| 139 | +impl<F: FnOnce() -> String> From<&'static str> for MaybeLazy<str, F> { |
| 140 | + #[inline] |
| 141 | + fn from(s: &'static str) -> MaybeLazy<str, F> { |
| 142 | + MaybeLazy::borrowed(s) |
| 143 | + } |
| 144 | +} |
0 commit comments