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| author | Yuki Okushi <huyuumi.dev@gmail.com> | 2020-01-29 18:56:22 +0900 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2020-01-29 18:56:22 +0900 |
| commit | 36fd7b9a5960a799dbfa41b032094c2b0a22143d (patch) | |
| tree | 0f4de127f25ecbb8b162fa0a5b7cf0a06afded22 | |
| parent | 343432a74d1b92e4d3e71de4271e68304e046da3 (diff) | |
| parent | f722964d00f9276b86777fab8db3fbfecd440ae7 (diff) | |
| download | rust-36fd7b9a5960a799dbfa41b032094c2b0a22143d.tar.gz rust-36fd7b9a5960a799dbfa41b032094c2b0a22143d.zip | |
Rollup merge of #67722 - petertodd:2019-improve-any-comment, r=Mark-Simulacrum
Minor: note how Any is an unsafe trait in SAFETY comments Motivation: helpful to people like myself reading the standard library source to better understand how to use Any, especially if we do go ahead with https://github.com/rust-lang/rust/pull/67562 and make it an unsafe trait.
| -rw-r--r-- | src/libcore/any.rs | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/src/libcore/any.rs b/src/libcore/any.rs index af02e84d3fa..97ef513cbcc 100644 --- a/src/libcore/any.rs +++ b/src/libcore/any.rs @@ -194,7 +194,9 @@ impl dyn Any { #[inline] pub fn downcast_ref<T: Any>(&self) -> Option<&T> { if self.is::<T>() { - // SAFETY: just checked whether we are pointing to the correct type + // SAFETY: just checked whether we are pointing to the correct type, and we can rely on + // that check for memory safety because we have implemented Any for all types; no other + // impls can exist as they would conflict with our impl. unsafe { Some(&*(self as *const dyn Any as *const T)) } } else { None @@ -228,7 +230,9 @@ impl dyn Any { #[inline] pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { if self.is::<T>() { - // SAFETY: just checked whether we are pointing to the correct type + // SAFETY: just checked whether we are pointing to the correct type, and we can rely on + // that check for memory safety because we have implemented Any for all types; no other + // impls can exist as they would conflict with our impl. unsafe { Some(&mut *(self as *mut dyn Any as *mut T)) } } else { None |