Valen's Borrow Checker Lets Multiple References Mutate the Same Data

Valen's Memory Safety: A New Kind of Borrow Checking

Valen introduces a flexible borrow checker based on group borrowing, which relaxes the shared-xor-mutable rule to only prevent use-after-free. The compiler tracks where each reference points, allowing patterns like multiple mutable references to the same object—common in C++ but previously impossible to check at compile time. This approach has already influenced Carbon, Ante, and other languages, and Valen aims to interoperate with Rust.