Note the invariance over 'env in Scope<'env>.

m-ou-se · m-ou-se · commit aa9c0881efb1 · 2022-01-05T12:14:32.000+01:00
diff --git a/library/std/src/thread/scoped.rs b/library/std/src/thread/scoped.rs
@@ -11,6 +11,8 @@ use crate::sync::Arc;
 /// See [`scope`] for details.
 pub struct Scope<'env> {
     data: ScopeData,
+    /// Invariance over 'env, to make sure 'env cannot shrink,
+    /// which is necessary for soundness.
     env: PhantomData<&'env mut &'env ()>,
 }
 

Original file line number	Diff line number	Diff line change
`@@ -11,6 +11,8 @@ use crate::sync::Arc;`
`11`	`11`	/// See [`scope`] for details.
`12`	`12`	`pub struct Scope<'env> {`
`13`	`13`	`data: ScopeData,`
	`14`	`+ /// Invariance over 'env, to make sure 'env cannot shrink,`
	`15`	`+ /// which is necessary for soundness.`
`14`	`16`	`env: PhantomData<&'env mut &'env ()>,`
`15`	`17`	`}`
`16`	`18`