From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Thu, 14 Nov 2024 22:15:26 +0000 (+0000)
Subject: attempt at sealing
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?a=commitdiff_plain;h=c65f6f71e3284439e3d3e0e06e699cfa1f1809f4;p=manually-boxed

attempt at sealing
---

diff --git a/src/lib.rs b/src/lib.rs
index b89da5d..55d3733 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -17,7 +17,7 @@ pub struct NoAliasSingleton {
 ///
 /// Implemented for `NoAliasSingleton` and the ZST reference tokens,
 /// and `&`-references to them.
-pub unsafe trait IsRefToken<'a>: Sized {
+pub unsafe trait IsRefToken<'a>: Sized + Sealed {
     /// Obtain a new ZST token from something that might be a real object.
     #[inline]
     fn ref_token(self) -> RefToken<'a> {
@@ -29,7 +29,7 @@ pub unsafe trait IsRefToken<'a>: Sized {
 ///
 /// Implemented for `NoAliasSingleton` and `MutToken`,
 /// and `&mut`-references to them.
-pub unsafe trait IsMutToken<'a>: IsRefToken<'a> + Sized {
+pub unsafe trait IsMutToken<'a>: IsRefToken<'a> + Sized + Sealed {
     /// Obtain a new ZST token from something that might be a real object.
     #[inline]
     fn mut_token<'r>(self) -> MutToken<'r>
@@ -57,20 +57,34 @@ pub unsafe trait IsMutToken<'a>: IsRefToken<'a> + Sized {
         }
     }
 }
-unsafe impl<'a> IsRefToken<'a> for &'a NoAliasSingleton {}
-unsafe impl<'a> IsRefToken<'a> for &'a mut NoAliasSingleton {}
-unsafe impl<'a> IsMutToken<'a> for &'a mut NoAliasSingleton {}
-unsafe impl<'a> IsRefToken<'a> for RefToken<'a> {}
-unsafe impl<'a> IsRefToken<'a> for MutToken<'a> {}
-unsafe impl<'a> IsMutToken<'a> for MutToken<'a> {}
-unsafe impl<'a, A: IsRefToken<'a>> IsRefToken<'a> for &'a A {}
-
-unsafe impl<'r, 'a, 'aa, A> IsRefToken<'r> for &'aa mut A
+
+mod sealed { pub trait Sealed {} }
+use sealed::Sealed;
+
+macro_rules! impl_is { { $(
+    unsafe impl [$($gens:tt)*] $trait:ty, for $ty:ty {}
+)* } => { $(
+    unsafe impl <$($gens   )*> $trait    for $ty    {}
+    impl        <$($gens   )*> Sealed    for $ty    {}
+)* } }
+impl_is! {
+
+unsafe impl['a] IsRefToken<'a>, for &'a NoAliasSingleton {}
+unsafe impl['a] IsRefToken<'a>, for &'a mut NoAliasSingleton {}
+unsafe impl['a] IsMutToken<'a>, for &'a mut NoAliasSingleton {}
+unsafe impl['a] IsRefToken<'a>, for RefToken<'a> {}
+unsafe impl['a] IsRefToken<'a>, for MutToken<'a> {}
+unsafe impl['a] IsMutToken<'a>, for MutToken<'a> {}
+unsafe impl['a, A: IsRefToken<'a>] IsRefToken<'a>, for &'a A {}
+
+unsafe impl['r, 'a, 'aa, A] IsRefToken<'r>, for &'aa mut A
 where A: IsMutToken<'a>, 'a: 'r, 'aa: 'r {}
 
-unsafe impl<'r, 'a, 'aa, A> IsMutToken<'r> for &'aa mut A
+unsafe impl['r, 'a, 'aa, A] IsMutToken<'r>, for &'aa mut A
 where A: IsMutToken<'a>, 'a: 'r, 'aa: 'r {}
 
+}
+
 /// `&NoAliasSingleton`, but a ZST
 ///
 /// We don't actually ever need to look at the data for the singleton.