src/any.rs - anymap blob - Chris Morgan’s Git repositories

   1 //! The different types of `Any` for use in a map.
   2 //!
   3 //! This stuff is all based on `std::any`, but goes a little further, with `CloneAny` being a
   4 //! cloneable `Any` and with the `Send` and `Sync` bounds possible on both `Any` and `CloneAny`.
   5
   6 use std::fmt;
   7 use std::any::Any;
   8
   9 #[doc(hidden)]
  10 pub trait CloneToAny {
  11     /// Clone `self` into a new `Box<dyn CloneAny>` object.
  12     fn clone_to_any(&self) -> Box<dyn CloneAny>;
  13 }
  14
  15 impl<T: Any + Clone> CloneToAny for T {
  16     #[inline]
  17     fn clone_to_any(&self) -> Box<dyn CloneAny> {
  18         Box::new(self.clone())
  19     }
  20 }
  21
  22 macro_rules! impl_clone {
  23     ($t:ty) => {
  24         impl Clone for Box<$t> {
  25             #[inline]
  26             fn clone(&self) -> Box<$t> {
  27                 // SAFETY: this dance is to reapply any Send/Sync marker. I’m not happy about this
  28                 // approach, given that I used to do it in safe code, but then came a dodgy
  29                 // future-compatibility warning where_clauses_object_safety, which is spurious for
  30                 // auto traits but still super annoying (future-compatibility lints seem to mean
  31                 // your bin crate needs a corresponding allow!). Although I explained my plight¹
  32                 // and it was all explained and agreed upon, no action has been taken. So I finally
  33                 // caved and worked around it by doing it this way, which matches what’s done for
  34                 // std::any², so it’s probably not *too* bad.
  35                 //
  36                 // ¹ https://github.com/rust-lang/rust/issues/51443#issuecomment-421988013
  37                 // ² https://github.com/rust-lang/rust/blob/e7825f2b690c9a0d21b6f6d84c404bb53b151b38/library/alloc/src/boxed.rs#L1613-L1616
  38                 let clone: Box<dyn CloneAny> = (**self).clone_to_any();
  39                 let raw: *mut dyn CloneAny = Box::into_raw(clone);
  40                 unsafe { Box::from_raw(raw as *mut $t) }
  41             }
  42         }
  43
  44         impl fmt::Debug for $t {
  45             #[inline]
  46             fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  47                 f.pad(stringify!($t))
  48             }
  49         }
  50     }
  51 }
  52
  53 #[allow(missing_docs)]  // Bogus warning (it’s not public outside the crate), ☹
  54 pub trait UncheckedAnyExt: Any {
  55     unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T;
  56     unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T;
  57     unsafe fn downcast_unchecked<T: Any>(self: Box<Self>) -> Box<T>;
  58 }
  59
  60 #[doc(hidden)]
  61 /// A trait for the conversion of an object into a boxed trait object.
  62 pub trait IntoBox<A: ?Sized + UncheckedAnyExt>: Any {
  63     /// Convert self into the appropriate boxed form.
  64     fn into_box(self) -> Box<A>;
  65 }
  66
  67 macro_rules! implement {
  68     ($base:ident, $(+ $bounds:ident)*) => {
  69         impl UncheckedAnyExt for dyn $base $(+ $bounds)* {
  70             #[inline]
  71             unsafe fn downcast_ref_unchecked<T: 'static>(&self) -> &T {
  72                 &*(self as *const Self as *const T)
  73             }
  74
  75             #[inline]
  76             unsafe fn downcast_mut_unchecked<T: 'static>(&mut self) -> &mut T {
  77                 &mut *(self as *mut Self as *mut T)
  78             }
  79
  80             #[inline]
  81             unsafe fn downcast_unchecked<T: 'static>(self: Box<Self>) -> Box<T> {
  82                 Box::from_raw(Box::into_raw(self) as *mut T)
  83             }
  84         }
  85
  86         impl<T: $base $(+ $bounds)*> IntoBox<dyn $base $(+ $bounds)*> for T {
  87             #[inline]
  88             fn into_box(self) -> Box<dyn $base $(+ $bounds)*> {
  89                 Box::new(self)
  90             }
  91         }
  92     }
  93 }
  94
  95 implement!(Any,);
  96 implement!(Any, + Send);
  97 implement!(Any, + Send + Sync);
  98
  99 /// [`Any`], but with cloning.
 100 ///
 101 /// Every type with no non-`'static` references that implements `Clone` implements `CloneAny`.
 102 /// See [`std::any`] for more details on `Any` in general.
 103 pub trait CloneAny: Any + CloneToAny { }
 104 impl<T: Any + Clone> CloneAny for T { }
 105 implement!(CloneAny,);
 106 implement!(CloneAny, + Send);
 107 implement!(CloneAny, + Send + Sync);
 108 impl_clone!(dyn CloneAny);
 109 impl_clone!(dyn CloneAny + Send);
 110 impl_clone!(dyn CloneAny + Send + Sync);