Skip type checking in from-Any casting.

We know the type with certainty already.
This should make a microscopic improvement in perf.
This commit is contained in:
Chris Morgan 2014-06-12 22:59:03 +10:00
parent 6bd64ec070
commit 8c1b4578cc

View file

@ -11,10 +11,12 @@
#[cfg(test)]
extern crate test;
use std::any::{Any, AnyRefExt, AnyMutRefExt};
use std::any::Any;
use std::intrinsics::TypeId;
use std::collections::HashMap;
use std::hash::{Hash, Hasher, Writer};
use std::mem::{transmute, transmute_copy};
use std::raw::TraitObject;
struct TypeIdHasher;
@ -29,7 +31,7 @@ impl Writer for TypeIdState {
debug_assert!(bytes.len() == 8);
unsafe {
std::ptr::copy_nonoverlapping_memory(&mut self.value,
std::mem::transmute(&bytes[0]),
transmute(&bytes[0]),
1)
}
}
@ -45,6 +47,42 @@ impl Hasher<TypeIdState> for TypeIdHasher {
}
}
/// An extension of `AnyRefExt` allowing unchecked downcasting of trait objects to `&T`.
trait UncheckedAnyRefExt<'a> {
/// Returns a reference to the boxed value, assuming that it is of type `T`. This should only be
/// called if you are ABSOLUTELY CERTAIN of `T` as you will get really wacky output if its not.
unsafe fn as_ref_unchecked<T: 'static>(self) -> &'a T;
}
impl<'a> UncheckedAnyRefExt<'a> for &'a Any {
#[inline]
unsafe fn as_ref_unchecked<T: 'static>(self) -> &'a T {
// Get the raw representation of the trait object
let to: TraitObject = transmute_copy(&self);
// Extract the data pointer
transmute(to.data)
}
}
/// An extension of `AnyMutRefExt` allowing unchecked downcasting of trait objects to `&mut T`.
trait UncheckedAnyMutRefExt<'a> {
/// Returns a reference to the boxed value, assuming that it is of type `T`. This should only be
/// called if you are ABSOLUTELY CERTAIN of `T` as you will get really wacky output if its not.
unsafe fn as_mut_unchecked<T: 'static>(self) -> &'a mut T;
}
impl<'a> UncheckedAnyMutRefExt<'a> for &'a mut Any {
#[inline]
unsafe fn as_mut_unchecked<T: 'static>(self) -> &'a mut T {
// Get the raw representation of the trait object
let to: TraitObject = transmute_copy(&self);
// Extract the data pointer
transmute(to.data)
}
}
/// A map containing zero or one values for any given type and allowing convenient,
/// type-safe access to those values.
///
@ -86,12 +124,12 @@ impl AnyMap {
impl AnyMap {
/// Retrieve the value stored in the map for the type `T`, if it exists.
pub fn find<'a, T: 'static>(&'a self) -> Option<&'a T> {
self.data.find(&TypeId::of::<T>()).and_then(|any| any.as_ref::<T>())
self.data.find(&TypeId::of::<T>()).map(|any| unsafe { any.as_ref_unchecked::<T>() })
}
/// Retrieve a mutable reference to the value stored in the map for the type `T`, if it exists.
pub fn find_mut<'a, T: 'static>(&'a mut self) -> Option<&'a mut T> {
self.data.find_mut(&TypeId::of::<T>()).and_then(|any| any.as_mut::<T>())
self.data.find_mut(&TypeId::of::<T>()).map(|any| unsafe { any.as_mut_unchecked::<T>() })
}
/// Set the value contained in the map for the type `T`.