add note regarding unsafe blocks and place expressions

[web.git] / personal / _posts / 2018-08-22-two-kinds-of-invariants.md

diff --git a/personal/_posts/2018-08-22-two-kinds-of-invariants.md b/personal/_posts/2018-08-22-two-kinds-of-invariants.md
index 34f33bb9c0a788803459d4be020eb2de79b2050c..fcf12ea1394dcea6b7c699d86e624f74c2ef1040 100644 (file)
--- a/personal/_posts/2018-08-22-two-kinds-of-invariants.md
+++ b/personal/_posts/2018-08-22-two-kinds-of-invariants.md
@@ -72,7 +72,7 @@ For `Vec` to work, however, `ptr` will be pointing to valid memory of size `cap
 This is an invariant that all the unsafe code implementing `Vec` maintains, and it is the invariant that the safe API surface of `Vec` expects the outside world to uphold.
 The reason this works is that the fields mentioned in this invariant are all private, so safe code cannot break the invariant and use that broken invariant to cause havoc.
 Again, the safety invariant is about ensuring safe execution of safe code.
-Unsafe code can of course break this invariant, but then it us just Doing It Wrong (TM).
+Unsafe code can of course break this invariant, but then it is just Doing It Wrong (TM).
 
 Thanks to privacy and an abstraction barrier, types in Rust can define *their own safety invariant*, and they can then expect the outside world to respect that invariant.
 As we have seen with `Vec`, when generic types are involved, these custom safety invariants will often have a "structural" element in that being safe at `Vec<T>` is defined in terms of being safe at `T`.