Hi,
I hope this question is not too specific for the mailing list, but I
stumbled upon something I don't understand today and thought I'd better ask.
In librustc/middle/ty.rs there is the mk_t() function which creates and
caches objects of type "t" from values of type "sty". However, the way
it uses the cache seems kind of strange, especially the key creation at
the beginning:
fn mk_t(cx: ctxt, st: sty) -> t {
// Check for primitive types.
// ... omitted here ...
let key = intern_key { sty: to_unsafe_ptr(&st) };
match cx.interner.find(&key) {
Some(t) => unsafe { return cast::transmute(&t.sty); },
_ => ()
}
The intern_key is created by taking a pointer to "st", which in effect
is the address of the argument slot on the stack. That can't be right,
can it? Is it possible that this cache is actually never used and the
compiler always creates new t_box_ instances every time mk_t() is called
somewhere?
I don't know how bad this would be, maybe mk_t() is only called once per
unique type anyway. Or maybe I'm overlooking something here?
Any insight on this would be appreciated :)
Cheers,
Michael
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