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

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