rune/runtime/
fmt.rs

1use core::ptr::NonNull;
2
3use crate::alloc::fmt::TryWrite;
4use crate::alloc::{self, String};
5use crate::runtime::VmResult;
6use crate::Any;
7
8/// A formatter for the rune virtual machine.
9///
10/// This is used as a receiver to functions implementing the [`DEBUG_FMT`]
11/// and [`DISPLAY_FMT`] protocols.
12///
13/// [`DEBUG_FMT`]: crate::runtime::Protocol::DEBUG_FMT
14/// [`DISPLAY_FMT`]: crate::runtime::Protocol::DISPLAY_FMT
15#[derive(Any)]
16#[rune(crate, item = ::std::fmt)]
17pub struct Formatter {
18    pub(crate) out: NonNull<dyn TryWrite>,
19    pub(crate) buf: String,
20}
21
22impl Formatter {
23    /// Format onto the given trywrite.
24    pub(crate) fn format_with(
25        out: &mut String,
26        f: impl FnOnce(&mut Self) -> VmResult<()>,
27    ) -> VmResult<()> {
28        // SAFETY: Call to this function ensures that the formatter does not
29        // outlive the passed in reference.
30        let mut fmt = Formatter {
31            out: NonNull::from(out),
32            buf: String::new(),
33        };
34        f(&mut fmt)
35    }
36
37    #[inline]
38    pub(crate) fn parts_mut(&mut self) -> (&mut dyn TryWrite, &str) {
39        // SAFETY: Formatter constrution requires `out` to be valid.
40        (unsafe { self.out.as_mut() }, &self.buf)
41    }
42
43    #[inline]
44    pub(crate) fn buf_mut(&mut self) -> &mut String {
45        &mut self.buf
46    }
47}
48
49impl TryWrite for Formatter {
50    #[inline]
51    fn try_write_str(&mut self, s: &str) -> alloc::Result<()> {
52        // SAFETY: Formatter constrution requires `out` to be valid.
53        unsafe { self.out.as_mut().try_write_str(s) }
54    }
55
56    #[inline]
57    fn try_write_char(&mut self, c: char) -> alloc::Result<()> {
58        // SAFETY: Formatter constrution requires `out` to be valid.
59        unsafe { self.out.as_mut().try_write_char(c) }
60    }
61}