On Borrow Checking

[Richard (Rikki) Andrew Cattermole]

On 11/05/2025 11:40 AM, Walter Bright wrote:
>     No multiple output support, which severely limits its capabilities.
> 
> It does not severely limit it. Even the Rust manual says it's a rare 
> case. It's a minor inconvenience that can be refactored away.

So I'm watching a video on Swift memory safety that Serg posted, and as 
it turns out Clang has a solution to this!

https://fosdem.org/2025/schedule/event/fosdem-2025-6176-incremental-memory-safety-in-an-established-software-stack-lessons-learned-from-swift/

For escaping through another parameter: 
https://clang.llvm.org/docs/AttributeReference.html#lifetime-capture-by

For escaping out the return value: 
https://clang.llvm.org/docs/AttributeReference.html#id8

The clang way:

```c
void addToSet(std::string_view a [[clang::lifetime_capture_by(s)]], 
std::set<std::string_view>& s) {
   s.insert(a);
}

struct string {
   // The returned pointer should not outlive ``*this``.
   const char *data() const [[clang::lifetimebound]];
};
```

My way (ignoring the lack of inferration):

```d
void addToSet(@escape(s=) string a, ref bool[string] s) {
	set[a] = true;
}

struct string {
	const char* data() const return&;
}
```