Re: [PATCH v3] rust: str: add {make,to}_{upper,lower}case() to CString

[Danilo Krummrich]

On 2/16/24 17:53, Alice Ryhl wrote:
> > +    pub fn make_ascii_lowercase(&mut self) {
> > +        self.0.make_ascii_lowercase();
> > +    }
>
> It's important to note here that this doesn't remove or introduce NUL
> bytes.
>
> pub fn make_ascii_lowercase(&mut self) {
>      // INVARIANT: This doesn't introduce or remove NUL bytes in the c
>      // string.
>      self.0.make_ascii_lowercase();
> }
>
> Ditto for make_ascii_uppercase. (But not the to_* methods.)
>
> > +    /// Returns a copy of this [`CString`] where each character is mapped to its
> > +    /// ASCII lower case equivalent.
> > +    ///
> > +    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
> > +    /// but non-ASCII letters are unchanged.
> > +    ///
> > +    /// To lowercase the value in-place, use [`make_ascii_lowercase`].
> > +    ///
> > +    /// [`make_ascii_lowercase`]: str::make_ascii_lowercase
> > +    pub fn to_ascii_lowercase(&self) -> Result<CString, AllocError> {
> > +        let mut s = (*self).to_cstring()?;
> > +
> > +        s.make_ascii_lowercase();
> > +
> > +        return Ok(s);
> > +    }
> > +
> > +    /// Returns a copy of this [`CString`] where each character is mapped to its
> > +    /// ASCII upper case equivalent.
> > +    ///
> > +    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
> > +    /// but non-ASCII letters are unchanged.
> > +    ///
> > +    /// To uppercase the value in-place, use [`make_ascii_uppercase`].
> > +    ///
> > +    /// [`make_ascii_uppercase`]: str::make_ascii_uppercase
> > +    pub fn to_ascii_uppercase(&self) -> Result<CString, AllocError> {
> > +        let mut s = (*self).to_cstring()?;
> > +
> > +        s.make_ascii_uppercase();
> > +
> > +        return Ok(s);
> > +    }
>
> Please move these to `CStr` as well.

That would result into two copies if I actually want a CString, wouldn't it?

Also, what would be the use case? And even if someone wants to have a CStr
again, couldn't we just deref the resulting CString?

- Danilo

> > +impl DerefMut for CString {
> > +    fn deref_mut(&mut self) -> &mut Self::Target {
> > +        unsafe { CStr::from_bytes_with_nul_unchecked_mut(&mut *self.buf) }
> > +    }
> > +}
>
> Needs a safety comment.
>
> impl DerefMut for CString {
>      fn deref_mut(&mut self) -> &mut Self::Target {
>          // SAFETY: A `CString` is always NUL-terminated and contains no
> 	// other NUL bytes.
>          unsafe { CStr::from_bytes_with_nul_unchecked_mut(&mut *self.buf) }
>      }
> }
>
> Alice