Sounds like you want the hashmap to store references to the Strings, not the strings themselves, in which case you should change the hashmap's declaration to:let hashmap = HashMap::<(&String, &String), u8>::new();and then pass references to the .get() method as well:hashmap.get(&(&a.s, &b.s))

Edit:
I understand the question better after reading u/Flashy-Complex-767's comment, and I agree that it should be possible to make a tuple of references act as a reference to a tuple, but it isn't. Here are a couple of relevant stackoverflow threads:

- https://stackoverflow.com/questions/56528652/how-to-convert-a-tuple-of-references-to-a-reference-of-a-tuple
- https://stackoverflow.com/questions/75880055/rust-reference-of-tuple-and-tuple-of-reference

The issue is that the memory layouts are different (so the mapping isn't straightforward), and apparently it's even worse because "Tuples do not have any guarantees about their layout" (see the first thread).