add slice const conversion

Author: TheNumbat

README.md

@@ -285,6 +285,7 @@ For faster parallel builds, you can instead generate [ninja](https://ninja-build
 - Types
     - [ ] Result<T,E>
     - [ ] Map: don't store hashes of integer keys
+    - [ ] Opt: specializations for null representations
 - Allocators
     - [ ] Per-thread pools
 - Misc

rpp/slice.h

@@ -45,6 +45,12 @@ struct Slice {
         length_ = init.size();
     }
 
+    operator Slice<const T>() const noexcept
+        requires(!Const<T>)
+    {
+        return Slice<const T>{data_, length_};
+    }
+
     constexpr Slice(const Slice& src) noexcept = default;
     constexpr Slice& operator=(const Slice& src) noexcept = default;
 

test/arrays.cpp

@@ -106,6 +106,8 @@ i32 main() {
         static_assert(Same<decltype(deduct4), Slice<i32>>);
         auto deduct5 = constv.slice();
         static_assert(Same<decltype(deduct5), Slice<const i32>>);
+        auto deduct6 = Slice<const i32>{deduct4};
+        static_assert(Same<decltype(deduct6), Slice<const i32>>);
 
         v.pop();
         assert(v.length() == 2);