---

yaml
---
r: 217038
b: refs/heads/stable
c: b2f486f
h: refs/heads/master
v: v3

Author: Nick Hamann

[refs]

@@ -29,5 +29,5 @@ refs/heads/tmp: 378a370ff2057afeb1eae86eb6e78c476866a4a6
 refs/tags/1.0.0-alpha.2: 4c705f6bc559886632d3871b04f58aab093bfa2f
 refs/tags/homu-tmp: a5286998df566e736b32f6795bfc3803bdaf453d
 refs/tags/1.0.0-beta: 8cbb92b53468ee2b0c2d3eeb8567005953d40828
-refs/heads/stable: 857a12a01ed8a9249cea8f48b39a0f8bdfd95cbd
+refs/heads/stable: b2f486feafa99124479d1b5e74c9acc6ed7cc233
 refs/tags/1.0.0: 55bd4f8ff2b323f317ae89e254ce87162d52a375

branches/stable/src/doc/reference.md

@@ -3510,13 +3510,21 @@ more of the closure traits:
 
 ### Trait objects
 
-Every trait item (see [traits](#traits)) defines a type with the same name as
-the trait. This type is called the _trait object_ of the trait. Trait objects
-permit "late binding" of methods, dispatched using _virtual method tables_
-("vtables"). Whereas most calls to trait methods are "early bound" (statically
-resolved) to specific implementations at compile time, a call to a method on an
-trait objects is only resolved to a vtable entry at compile time. The actual
-implementation for each vtable entry can vary on an object-by-object basis.
+In Rust, a type like `&SomeTrait` or `Box<SomeTrait>` is called a _trait object_.
+Each instance of a trait object includes:
+
+ - a pointer to an instance of a type `T` that implements `SomeTrait`
+ - a _virtual method table_, often just called a _vtable_, which contains, for
+   each method of `SomeTrait` that `T` implements, a pointer to `T`'s
+   implementation (i.e. a function pointer).
+
+The purpose of trait objects is to permit "late binding" of methods. A call to
+a method on a trait object is only resolved to a vtable entry at compile time.
+The actual implementation for each vtable entry can vary on an object-by-object
+basis.
+
+Note that for a trait object to be instantiated, the trait must be
+_object-safe_. Object safety rules are defined in [RFC 255][rfc255].
 
 Given a pointer-typed expression `E` of type `&T` or `Box<T>`, where `T`
 implements trait `R`, casting `E` to the corresponding pointer type `&R` or