There is a lot of C++ code out there. A lot of it was not written by people who understand performance or who care. It is very easy to take that kind of code and make it faster, even without a switch to Rust.
The examples I have seen where a Rust rewrite is faster than original C++ code usually have glaring performance issues in the C++: Often, it is code that does a ton of unnecessary copies. The Rust code often doesn't copy as much because the Rust language makes that kind of copying inconvenient or because the person doing the rewrite is a Rust expert and not a C++ expert. The other kind of speedup I have seen is when people swap a C++ std::map for a Rust btree_map, and don't realize that absl::btree_map (a C++ btree map in Google's library) is what Rust's btree_map is based on.
I haven't seen any examples where C or C++ code written with performance in mind gets a rewrite to Rust and goes faster, and I have seen the opposite.
The examples I have seen where a Rust rewrite is faster than original C++ code usually have glaring performance issues in the C++: Often, it is code that does a ton of unnecessary copies. The Rust code often doesn't copy as much because the Rust language makes that kind of copying inconvenient or because the person doing the rewrite is a Rust expert and not a C++ expert. The other kind of speedup I have seen is when people swap a C++ std::map for a Rust btree_map, and don't realize that absl::btree_map (a C++ btree map in Google's library) is what Rust's btree_map is based on.
I haven't seen any examples where C or C++ code written with performance in mind gets a rewrite to Rust and goes faster, and I have seen the opposite.