71 lines
2.3 KiB
Rust
71 lines
2.3 KiB
Rust
use std::any::Any;
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// NOTE: This is `pub`, but isn't actually exposed outside the crate.
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// NOTE: Marked as `#[doc(hidden)]` and underscored, because they can be quite difficult to use
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// correctly, see discussion in #4160.
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// FIXME: Remove and replace with a coercion once rust-lang/rust#65991 is in MSRV (1.86).
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#[doc(hidden)]
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pub trait AsAny: Any {
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#[doc(hidden)]
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fn __as_any(&self) -> &dyn Any;
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#[doc(hidden)]
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fn __as_any_mut(&mut self) -> &mut dyn Any;
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#[doc(hidden)]
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fn __into_any(self: Box<Self>) -> Box<dyn Any>;
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}
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impl<T: Any> AsAny for T {
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#[inline(always)]
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fn __as_any(&self) -> &dyn Any {
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self
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}
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#[inline(always)]
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fn __as_any_mut(&mut self) -> &mut dyn Any {
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self
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}
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#[inline(always)]
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fn __into_any(self: Box<Self>) -> Box<dyn Any> {
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self
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}
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}
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#[macro_export]
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macro_rules! impl_dyn_casting {
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($trait:ident) => {
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impl dyn $trait + '_ {
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/// Downcast to the backend concrete type.
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///
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/// Returns `None` if the object was not from that backend.
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pub fn cast_ref<T: $trait>(&self) -> Option<&T> {
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let this: &dyn std::any::Any = self.__as_any();
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this.downcast_ref::<T>()
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}
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/// Mutable downcast to the backend concrete type.
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///
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/// Returns `None` if the object was not from that backend.
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pub fn cast_mut<T: $trait>(&mut self) -> Option<&mut T> {
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let this: &mut dyn std::any::Any = self.__as_any_mut();
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this.downcast_mut::<T>()
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}
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/// Owned downcast to the backend concrete type.
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///
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/// Returns `Err` with `self` if the object was not from that backend.
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pub fn cast<T: $trait>(self: Box<Self>) -> Result<Box<T>, Box<Self>> {
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let reference: &dyn std::any::Any = self.__as_any();
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if reference.is::<T>() {
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let this: Box<dyn std::any::Any> = self.__into_any();
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// Unwrap is okay, we just checked the type of `self` is `T`.
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Ok(this.downcast::<T>().unwrap())
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} else {
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Err(self)
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}
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}
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}
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};
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}
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pub use impl_dyn_casting;
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