In situ parsing

[dtolnay]

pub fn from_mut_str<'a, T>(s: &'a mut str) -> Result<T>
where
    T: Deserialize<'a>;

Strings with escape sequences are decoded in place!

// before
"{\"msg\":\"abc\\nxyz\"}"

// after
"{\"msg\":\"abc\nxyzz\"}"
            ^^^^^^^^ output &str

[lambda-fairy]

&[u8], &[Option<u8>], and &[u16] can be decoded in place as well, since every element of a JSON array takes up at least two bytes. With some effort this can apply to tuples and structs too.

I can imagine doing something clever to represent maps, but that might be going a bit too far.

[clarfonthey]

What would happen to the end of the string here? Because the result is shorter than the actual buffer.

Would the input itself have any guarantees?

[dtolnay]

There are no guarantees around what modification is made to the input string. In the example above, b'z' happens to be duplicated to account for the difference in length.

[clarfonthey]

Oh, I see. I missed the single b'z' so it looked like the string was shortened, which didn't seem right.

[saethlin]

This would be pretty cool. Does anyone have an implementation of this in-place (and no_std) unescaping? I can't find one, but maybe my google-fu just isn't good enough.

EDIT: Got a prototype working. This was much easier than I thought, just needed some time to think on it.