Hi Philip, On Fri, Sep 24, 2021 at 12:01:42PM +0100, Philip Herron wrote: > This is really useful information, will this mean that the lexer token will > need to represent strings differently as well? Or is the std::string in the > lexer still ok?
I think the respresentation as std::string is fine. As long as we don't mix std::strings between different types (byte strings may contain sequences of chars that aren't valid utf-8 sequenecs). > The change you made above has the problem that reference types like, arrays > are forms of what rust calls covariant types since they might contain an > inference variable, so they require lookup to determine the base type. Its > likely there is a reference cycle here. Though this change will not be > correct for type checking purposes. The design of the type system is purely > about rust type checking and inferring types. OK, so how do I represent an reference to an array type that doesn't contain any inference variables? When we see a b"hello" byte string that is the same as seeing &[b'h', b'e', b'l', b'l', b'o'] which is the same as seeing &[0x68u8, 0x65u8, 0x6cu8, 0x6cu8, 0x6fu8]; So we know this is &[u8;5] and if we write: let a = b"hello"; We want to infer that a has type &[u8;5]. > So for example this change will break the case of: > > ``` > let a:str = "test"; > ``` > > Since the TypePath of str can't know the size of the expected array at > compilation time. And the error message will end up with something like > "expected str got [i8, 4]"; Right, but that is for "proper strings". It is somewhat unfortunate that Rust calls byte strings also "strings", but they really aren't. b"abc" is static array of u8, not a &str (containing utf-8). I have to think about the slicing of "proper strings", which sound more complicated than slicing of byte strings, because I don't think you want to chop up a utf-8 sequence. For now I would simply try to get the type of byte strings like b"test" correct. Cheers, Mark -- Gcc-rust mailing list Gcc-rust@gcc.gnu.org https://gcc.gnu.org/mailman/listinfo/gcc-rust
