From: Simon Tatham <anakin@pobox.com>
Date: Thu, 10 Apr 2025 11:55:25 +0000 (+0100)
Subject: Allow converting back into slice references.
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?a=commitdiff_plain;h=318ff12bebef5050c79374431039a7e5a84f53be;p=nimber.git

Allow converting back into slice references.
---

diff --git a/src/finitenimber.rs b/src/finitenimber.rs
index 828ee64..610fa3d 100644
--- a/src/finitenimber.rs
+++ b/src/finitenimber.rs
@@ -4,14 +4,21 @@ use std::ops::BitXor;
 pub trait FiniteNimberBase:
     BitXor<Output = Self::Owned> + Eq + Debug + Sized
 {
+    type Cheap<'a>: FiniteNimberBase where Self: 'a;
     type Owned: FiniteNimberBase + Clone;
 
+    fn to_cheap<'a>(&'a self) -> Self::Cheap<'a>;
     fn to_owned(self) -> Self::Owned;
 }
 
 impl FiniteNimberBase for u64 {
+    type Cheap<'a> = Self where Self: 'a;
     type Owned = Self;
 
+    fn to_cheap<'a>(&'a self) -> Self::Cheap<'a> {
+        *self
+    }
+
     fn to_owned(self) -> Self::Owned {
         self
     }
@@ -52,16 +59,26 @@ impl BitXor for IntSlice<'_> {
 }
 
 impl FiniteNimberBase for IntVector {
-    type Owned = Self;
+    type Cheap<'a> = IntSlice<'a> where Self: 'a;
+    type Owned = IntVector;
+
+    fn to_cheap<'a>(&'a self) -> Self::Cheap<'a> {
+        IntSlice(&self.0)
+    }
 
     fn to_owned(self) -> Self::Owned {
         self
     }
 }
 
-impl FiniteNimberBase for IntSlice<'_> {
+impl<'a> FiniteNimberBase for IntSlice<'a> {
+    type Cheap<'b> = IntSlice<'b> where Self: 'b;
     type Owned = IntVector;
 
+    fn to_cheap<'b>(&'b self) -> Self::Cheap<'b> {
+        IntSlice(self.0)
+    }
+
     fn to_owned(self) -> Self::Owned {
         IntVector(self.0.into())
     }